Added challenge middleware

2022-08-19 13:45:50 +01:00 · 2022-08-19 13:45:50 +01:00 · 1e55797ec8
parent 6b1a008719
commit 1e55797ec8
26 changed files with 2244 additions and 62 deletions
--- a/go.mod
+++ b/go.mod
@ -73,11 +73,15 @@ require (
 	go.uber.org/zap v1.22.0
 	golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e
 	golang.org/x/image v0.0.0-20210220032944-ac19c3e999fb
+	google.golang.org/protobuf v1.28.0
+	gopkg.in/go-playground/assert.v1 v1.2.1 // indirect
 	gopkg.in/go-playground/validator.v9 v9.31.0
 	gopkg.in/natefinch/lumberjack.v2 v2.0.0
 	olympos.io/encoding/edn v0.0.0-20201019073823-d3554ca0b0a3
 )

+require github.com/gorilla/sessions v1.2.1
+
 require (
 	github.com/PuerkitoBio/goquery v1.6.1 // indirect
 	github.com/RoaringBitmap/roaring v0.9.4 // indirect
@ -135,6 +139,7 @@ require (
 	github.com/golang/snappy v0.0.4 // indirect
 	github.com/google/btree v1.0.1 // indirect
 	github.com/google/gopacket v1.1.19 // indirect
+	github.com/gorilla/securecookie v1.1.1 // indirect
 	github.com/gorilla/websocket v1.5.0 // indirect
 	github.com/hashicorp/errwrap v1.1.0 // indirect
 	github.com/hashicorp/go-multierror v1.1.1 // indirect
@ -254,8 +259,6 @@ require (
 	golang.org/x/time v0.0.0-20220224211638-0e9765cccd65 // indirect
 	golang.org/x/tools v0.1.11 // indirect
 	golang.org/x/xerrors v0.0.0-20220609144429-65e65417b02f // indirect
-	google.golang.org/protobuf v1.28.0 // indirect
-	gopkg.in/go-playground/assert.v1 v1.2.1 // indirect
 	gopkg.in/natefinch/npipe.v2 v2.0.0-20160621034901-c1b8fa8bdcce // indirect
 	gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7 // indirect
 	gopkg.in/urfave/cli.v1 v1.20.0 // indirect
--- a/go.sum
+++ b/go.sum
@ -1056,6 +1056,10 @@ github.com/gorilla/mux v1.7.2/go.mod h1:1lud6UwP+6orDFRuTfBEV8e9/aOM/c4fVVCaMa2z
 github.com/gorilla/mux v1.7.3/go.mod h1:1lud6UwP+6orDFRuTfBEV8e9/aOM/c4fVVCaMa2zaAs=
 github.com/gorilla/mux v1.7.4/go.mod h1:DVbg23sWSpFRCP0SfiEN6jmj59UnW/n46BH5rLB71So=
 github.com/gorilla/mux v1.8.0/go.mod h1:DVbg23sWSpFRCP0SfiEN6jmj59UnW/n46BH5rLB71So=
+github.com/gorilla/securecookie v1.1.1 h1:miw7JPhV+b/lAHSXz4qd/nN9jRiAFV5FwjeKyCS8BvQ=
+github.com/gorilla/securecookie v1.1.1/go.mod h1:ra0sb63/xPlUeL+yeDciTfxMRAA+MP+HVt/4epWDjd4=
+github.com/gorilla/sessions v1.2.1 h1:DHd3rPN5lE3Ts3D8rKkQ8x/0kqfeNmBAaiSi+o7FsgI=
+github.com/gorilla/sessions v1.2.1/go.mod h1:dk2InVEVJ0sfLlnXv9EAgkf6ecYs/i80K/zI+bUmuGM=
 github.com/gorilla/websocket v0.0.0-20170926233335-4201258b820c/go.mod h1:E7qHFY5m1UJ88s3WnNqhKjPHQ0heANvMoAMk2YaljkQ=
 github.com/gorilla/websocket v1.4.0/go.mod h1:E7qHFY5m1UJ88s3WnNqhKjPHQ0heANvMoAMk2YaljkQ=
 github.com/gorilla/websocket v1.4.2/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
--- a/server/client.go
+++ b/server/client.go
@ -9,18 +9,22 @@ import (
 	"fmt"
 	"io/ioutil"
 	"net/http"
+	"net/http/cookiejar"
 	"net/url"
+
+	"github.com/btcsuite/btcutil/base58"
 )

 type PairingClient struct {
 	*http.Client
 	PayloadManager

-	baseAddress *url.URL
-	certPEM     []byte
-	serverPK    *ecdsa.PublicKey
-	serverMode  Mode
-	serverCert  *x509.Certificate
+	baseAddress     *url.URL
+	certPEM         []byte
+	serverPK        *ecdsa.PublicKey
+	serverMode      Mode
+	serverCert      *x509.Certificate
+	serverChallenge []byte
 }

 func NewPairingClient(c *ConnectionParams, config *PairingPayloadManagerConfig) (*PairingClient, error) {
@ -55,13 +59,18 @@ func NewPairingClient(c *ConnectionParams, config *PairingPayloadManagerConfig)
 		},
 	}

+	cj, err := cookiejar.New(nil)
+	if err != nil {
+		return nil, err
+	}
+
 	pm, err := NewPairingPayloadManager(c.aesKey, config)
 	if err != nil {
 		return nil, err
 	}

 	return &PairingClient{
-		Client:         &http.Client{Transport: tr},
+		Client:         &http.Client{Transport: tr, Jar: cj},
 		baseAddress:    u,
 		certPEM:        certPem,
 		serverCert:     serverCert,
@ -76,6 +85,10 @@ func (c *PairingClient) PairAccount() error {
 	case Receiving:
 		return c.sendAccountData()
 	case Sending:
+		err := c.getChallenge()
+		if err != nil {
+			return err
+		}
 		return c.receiveAccountData()
 	default:
 		return fmt.Errorf("unrecognised server mode '%d'", c.serverMode)
@ -84,21 +97,43 @@ func (c *PairingClient) PairAccount() error {

 func (c *PairingClient) sendAccountData() error {
 	c.baseAddress.Path = pairingReceive
-	_, err := c.Post(c.baseAddress.String(), "application/octet-stream", bytes.NewBuffer(c.PayloadManager.ToSend()))
+	resp, err := c.Post(c.baseAddress.String(), "application/octet-stream", bytes.NewBuffer(c.PayloadManager.ToSend()))
 	if err != nil {
 		return err
 	}

+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("status not ok, received '%s'", resp.Status)
+	}
+
 	return nil
 }

 func (c *PairingClient) receiveAccountData() error {
 	c.baseAddress.Path = pairingSend
-	resp, err := c.Get(c.baseAddress.String())
+	req, err := http.NewRequest(http.MethodGet, c.baseAddress.String(), nil)
 	if err != nil {
 		return err
 	}

+	if c.serverChallenge != nil {
+		ec, err := c.PayloadManager.EncryptPlain(c.serverChallenge)
+		if err != nil {
+			return err
+		}
+
+		req.Header.Set(sessionChallenge, base58.Encode(ec))
+	}
+
+	resp, err := c.Do(req)
+	if err != nil {
+		return err
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("status not ok, received '%s'", resp.Status)
+	}
+
 	payload, err := ioutil.ReadAll(resp.Body)
 	if err != nil {
 		return err
@ -106,3 +141,18 @@ func (c *PairingClient) receiveAccountData() error {

 	return c.PayloadManager.Receive(payload)
 }
+
+func (c *PairingClient) getChallenge() error {
+	c.baseAddress.Path = pairingChallenge
+	resp, err := c.Get(c.baseAddress.String())
+	if err != nil {
+		return err
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("status not ok, received '%s'", resp.Status)
+	}
+
+	c.serverChallenge, err = ioutil.ReadAll(resp.Body)
+	return err
+}
--- a/server/components_test.go
+++ b/server/components_test.go
@ -116,7 +116,7 @@ func (tpsc *TestPairingServerComponents) SetupPairingServerComponents(t *testing
 }

 type MockEncryptOnlyPayloadManager struct {
-	pem *PayloadEncryptionManager
+	*PayloadEncryptionManager
 }

 func NewMockEncryptOnlyPayloadManager(aesKey []byte) (*MockEncryptOnlyPayloadManager, error) {
@ -126,7 +126,7 @@ func NewMockEncryptOnlyPayloadManager(aesKey []byte) (*MockEncryptOnlyPayloadMan
 	}

 	return &MockEncryptOnlyPayloadManager{
-		pem: pem,
+		pem,
 	}, nil
 }

@ -138,21 +138,9 @@ func (m *MockEncryptOnlyPayloadManager) Mount() error {
 		return err
 	}

-	return m.pem.Encrypt(data)
+	return m.Encrypt(data)
 }

 func (m *MockEncryptOnlyPayloadManager) Receive(data []byte) error {
-	return m.pem.Decrypt(data)
-}
-
-func (m *MockEncryptOnlyPayloadManager) ToSend() []byte {
-	return m.pem.ToSend()
-}
-
-func (m *MockEncryptOnlyPayloadManager) Received() []byte {
-	return m.pem.Received()
-}
-
-func (m *MockEncryptOnlyPayloadManager) ResetPayload() {
-	m.pem.ResetPayload()
+	return m.Decrypt(data)
 }
--- a/server/handlers.go
+++ b/server/handlers.go
@ -1,14 +1,18 @@
 package server

 import (
+	"bytes"
+	"crypto/rand"
 	"database/sql"
 	"io/ioutil"
 	"net/http"
 	"time"

+	"github.com/btcsuite/btcutil/base58"
 	"go.uber.org/zap"

 	"github.com/status-im/status-go/ipfs"
+	"github.com/status-im/status-go/protocol/common"
 	"github.com/status-im/status-go/protocol/identity/identicon"
 	"github.com/status-im/status-go/protocol/images"
 )
@ -21,14 +25,19 @@ const (
 	ipfsPath       = "/ipfs"

 	// Handler routes for pairing
-	pairingBase    = "/pairing"
-	pairingSend    = pairingBase + "/send"
-	pairingReceive = pairingBase + "/receive"
+	pairingBase      = "/pairing"
+	pairingSend      = pairingBase + "/send"
+	pairingReceive   = pairingBase + "/receive"
+	pairingChallenge = pairingBase + "/challenge"
+
+	// Session names
+	sessionChallenge = "challenge"
+	sessionBlocked   = "blocked"
 )

 type HandlerPatternMap map[string]http.HandlerFunc

-func handleIdenticon(logger *zap.Logger) func(w http.ResponseWriter, r *http.Request) {
+func handleIdenticon(logger *zap.Logger) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		pks, ok := r.URL.Query()["publicKey"]
 		if !ok || len(pks) == 0 {
@ -52,7 +61,7 @@ func handleIdenticon(logger *zap.Logger) func(w http.ResponseWriter, r *http.Req
 	}
 }

-func handleImage(db *sql.DB, logger *zap.Logger) func(w http.ResponseWriter, r *http.Request) {
+func handleImage(db *sql.DB, logger *zap.Logger) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		messageIDs, ok := r.URL.Query()["messageId"]
 		if !ok || len(messageIDs) == 0 {
@ -85,7 +94,7 @@ func handleImage(db *sql.DB, logger *zap.Logger) func(w http.ResponseWriter, r *
 	}
 }

-func handleAudio(db *sql.DB, logger *zap.Logger) func(w http.ResponseWriter, r *http.Request) {
+func handleAudio(db *sql.DB, logger *zap.Logger) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		messageIDs, ok := r.URL.Query()["messageId"]
 		if !ok || len(messageIDs) == 0 {
@ -114,7 +123,7 @@ func handleAudio(db *sql.DB, logger *zap.Logger) func(w http.ResponseWriter, r *
 	}
 }

-func handleIPFS(downloader *ipfs.Downloader, logger *zap.Logger) func(w http.ResponseWriter, r *http.Request) {
+func handleIPFS(downloader *ipfs.Downloader, logger *zap.Logger) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		hashes, ok := r.URL.Query()["hash"]
 		if !ok || len(hashes) == 0 {
@ -140,7 +149,7 @@ func handleIPFS(downloader *ipfs.Downloader, logger *zap.Logger) func(w http.Res
 	}
 }

-func handlePairingReceive(ps *PairingServer) func(w http.ResponseWriter, r *http.Request) {
+func handlePairingReceive(ps *PairingServer) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		payload, err := ioutil.ReadAll(r.Body)
 		if err != nil {
@ -154,7 +163,8 @@ func handlePairingReceive(ps *PairingServer) func(w http.ResponseWriter, r *http
 	}
 }

-func handlePairingSend(ps *PairingServer) func(w http.ResponseWriter, r *http.Request) {
+func handlePairingSend(ps *PairingServer) http.HandlerFunc {
+	// TODO lock sending after one successful transfer
 	return func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/octet-stream")
 		_, err := w.Write(ps.PayloadManager.ToSend())
@ -163,3 +173,86 @@ func handlePairingSend(ps *PairingServer) func(w http.ResponseWriter, r *http.Re
 		}
 	}
 }
+
+func challengeMiddleware(ps *PairingServer, next http.Handler) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		s, err := ps.cookieStore.Get(r, sessionChallenge)
+		if err != nil {
+			ps.logger.Error("ps.cookieStore.Get(r, pairingStoreChallenge)", zap.Error(err))
+			http.Error(w, "error", http.StatusInternalServerError)
+		}
+
+		blocked, ok := s.Values[sessionBlocked].(bool)
+		if ok && blocked {
+			http.Error(w, "forbidden", http.StatusForbidden)
+			return
+		}
+
+		// If the request header doesn't include a challenge don't punish the client, just throw a 403
+		pc := r.Header.Get(sessionChallenge)
+		if pc == "" {
+			http.Error(w, "forbidden", http.StatusForbidden)
+			return
+		}
+
+		c, err := common.Decrypt(base58.Decode(pc), ps.ek)
+		if err != nil {
+			ps.logger.Error("c, err := common.Decrypt(rc, ps.ek)", zap.Error(err))
+			http.Error(w, "error", http.StatusInternalServerError)
+			return
+		}
+
+		// If the challenge is not in the session store don't punish the client, just throw a 403
+		challenge, ok := s.Values[sessionChallenge].([]byte)
+		if !ok {
+			http.Error(w, "forbidden", http.StatusForbidden)
+			return
+		}
+
+		// Only if we have both a challenge in the session store and in the request header
+		// do we entertain blocking the client. Because then we know someone is trying to be sneaky.
+		if bytes.Compare(c, challenge) != 0 {
+			s.Values[sessionBlocked] = true
+			err = s.Save(r, w)
+			if err != nil {
+				ps.logger.Error("err = s.Save(r, w)", zap.Error(err))
+			}
+
+			http.Error(w, "forbidden", http.StatusForbidden)
+			return
+		}
+
+		next.ServeHTTP(w, r)
+	}
+}
+
+func handlePairingChallenge(ps *PairingServer) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		s, err := ps.cookieStore.Get(r, sessionChallenge)
+		if err != nil {
+			ps.logger.Error("ps.cookieStore.Get(r, pairingStoreChallenge)", zap.Error(err))
+		}
+
+		var challenge []byte
+		challenge, ok := s.Values[sessionChallenge].([]byte)
+		if !ok {
+			challenge = make([]byte, 64)
+			_, err = rand.Read(challenge)
+			if err != nil {
+				ps.logger.Error("_, err = rand.Read(auth)", zap.Error(err))
+			}
+
+			s.Values[sessionChallenge] = challenge
+			err = s.Save(r, w)
+			if err != nil {
+				ps.logger.Error("err = s.Save(r, w)", zap.Error(err))
+			}
+		}
+
+		w.Header().Set("Content-Type", "application/octet-stream")
+		_, err = w.Write(challenge)
+		if err != nil {
+			ps.logger.Error("_, err = w.Write(challenge)", zap.Error(err))
+		}
+	}
+}
--- a/server/payload_manager.go
+++ b/server/payload_manager.go
@ -24,6 +24,7 @@ type PayloadManager interface {
 	ToSend() []byte
 	Received() []byte
 	ResetPayload()
+	EncryptPlain(plaintext []byte) ([]byte, error)
 }

 // PairingPayloadManagerConfig represents the initialisation parameters required for a PairingPayloadManager
@ -36,8 +37,8 @@ type PairingPayloadManagerConfig struct {

 // PairingPayloadManager is responsible for the whole lifecycle of a PairingPayload
 type PairingPayloadManager struct {
-	pp  *PairingPayload
-	pem *PayloadEncryptionManager
+	pp *PairingPayload
+	*PayloadEncryptionManager
 	ppm *PairingPayloadMarshaller
 	ppr PayloadRepository
 }
@ -53,10 +54,10 @@ func NewPairingPayloadManager(aesKey []byte, config *PairingPayloadManagerConfig
 	p := new(PairingPayload)

 	return &PairingPayloadManager{
-		pp:  p,
-		pem: pem,
-		ppm: NewPairingPayloadMarshaller(p),
-		ppr: NewPairingPayloadRepository(p, config),
+		pp:                       p,
+		PayloadEncryptionManager: pem,
+		ppm:                      NewPairingPayloadMarshaller(p),
+		ppr:                      NewPairingPayloadRepository(p, config),
 	}, nil
 }

@ -72,17 +73,17 @@ func (ppm *PairingPayloadManager) Mount() error {
 		return err
 	}

-	return ppm.pem.Encrypt(pb)
+	return ppm.Encrypt(pb)
 }

 // Receive takes a []byte representing raw data, parses and stores the data
 func (ppm *PairingPayloadManager) Receive(data []byte) error {
-	err := ppm.pem.Decrypt(data)
+	err := ppm.Decrypt(data)
 	if err != nil {
 		return err
 	}

-	err = ppm.ppm.UnmarshalProtobuf(ppm.pem.Received())
+	err = ppm.ppm.UnmarshalProtobuf(ppm.Received())
 	if err != nil {
 		return err
 	}
@ -90,20 +91,10 @@ func (ppm *PairingPayloadManager) Receive(data []byte) error {
 	return ppm.ppr.StoreToSource()
 }

-// ToSend returns the result of Mount
-func (ppm *PairingPayloadManager) ToSend() []byte {
-	return ppm.pem.ToSend()
-}
-
-// Received returns the decrypted input of Receive
-func (ppm *PairingPayloadManager) Received() []byte {
-	return ppm.pem.Received()
-}
-
 // ResetPayload resets all payload state managed by the PairingPayloadManager
 func (ppm *PairingPayloadManager) ResetPayload() {
 	ppm.pp.ResetPayload()
-	ppm.pem.ResetPayload()
+	ppm.PayloadEncryptionManager.ResetPayload()
 }

 // EncryptionPayload represents the plain text and encrypted text of payload data
@ -123,6 +114,10 @@ func NewPayloadEncryptionManager(aesKey []byte) (*PayloadEncryptionManager, erro
 	return &PayloadEncryptionManager{aesKey, new(EncryptionPayload), new(EncryptionPayload)}, nil
 }

+func (pem *PayloadEncryptionManager) EncryptPlain(plaintext []byte) ([]byte, error) {
+	return common.Encrypt(plaintext, pem.aesKey, rand.Reader)
+}
+
 func (pem *PayloadEncryptionManager) Encrypt(data []byte) error {
 	ep, err := common.Encrypt(data, pem.aesKey, rand.Reader)
 	if err != nil {
--- a/server/server_pairing.go
+++ b/server/server_pairing.go
@ -2,9 +2,12 @@ package server

 import (
 	"crypto/ecdsa"
+	"crypto/rand"
 	"crypto/tls"
 	"fmt"
 	"net"
+
+	"github.com/gorilla/sessions"
 )

 type PairingServer struct {
@ -14,6 +17,8 @@ type PairingServer struct {
 	pk   *ecdsa.PublicKey
 	ek   []byte
 	mode Mode
+
+	cookieStore *sessions.CookieStore
 }

 type Config struct {
@ -28,6 +33,22 @@ type Config struct {
 	*PairingPayloadManagerConfig
 }

+func makeCookieStore() (*sessions.CookieStore, error) {
+	auth := make([]byte, 64)
+	_, err := rand.Read(auth)
+	if err != nil {
+		return nil, err
+	}
+
+	enc := make([]byte, 32)
+	_, err = rand.Read(enc)
+	if err != nil {
+		return nil, err
+	}
+
+	return sessions.NewCookieStore(auth, enc), nil
+}
+
 // NewPairingServer returns a *PairingServer init from the given *Config
 func NewPairingServer(config *Config) (*PairingServer, error) {
 	pm, err := NewPairingPayloadManager(config.EK, config.PairingPayloadManagerConfig)
@ -35,6 +56,11 @@ func NewPairingServer(config *Config) (*PairingServer, error) {
 		return nil, err
 	}

+	cs, err := makeCookieStore()
+	if err != nil {
+		return nil, err
+	}
+
 	return &PairingServer{Server: NewServer(
 		config.Cert,
 		config.Hostname,
@ -42,7 +68,9 @@ func NewPairingServer(config *Config) (*PairingServer, error) {
 		pk:             config.PK,
 		ek:             config.EK,
 		mode:           config.Mode,
-		PayloadManager: pm}, nil
+		PayloadManager: pm,
+		cookieStore:    cs,
+	}, nil
 }

 // MakeConnectionParams generates a *ConnectionParams based on the Server's current state
@ -76,11 +104,17 @@ func (s *PairingServer) StartPairing() error {
 }

 func (s *PairingServer) startReceivingAccountData() error {
-	s.SetHandlers(HandlerPatternMap{pairingReceive: handlePairingReceive(s)})
+	s.SetHandlers(HandlerPatternMap{
+		pairingReceive:   handlePairingReceive(s),
+		pairingChallenge: handlePairingChallenge(s),
+	})
 	return s.Start()
 }

 func (s *PairingServer) startSendingAccountData() error {
-	s.SetHandlers(HandlerPatternMap{pairingSend: handlePairingSend(s)})
+	s.SetHandlers(HandlerPatternMap{
+		pairingSend:      challengeMiddleware(s, handlePairingSend(s)),
+		pairingChallenge: handlePairingChallenge(s),
+	})
 	return s.Start()
 }
--- a/server/server_pairing_test.go
+++ b/server/server_pairing_test.go
@ -2,6 +2,7 @@ package server

 import (
 	"crypto/ecdsa"
+	"crypto/rand"
 	"testing"
 	"time"

@ -85,13 +86,13 @@ func (s *PairingServerSuite) TestPairingServer_StartPairing() {

 		switch m {
 		case Receiving:
-			s.Require().Equal(c.PayloadManager.(*MockEncryptOnlyPayloadManager).pem.toSend.plain, s.PS.Received())
-			s.Require().Equal(s.PS.PayloadManager.(*MockEncryptOnlyPayloadManager).pem.received.encrypted, c.PayloadManager.(*MockEncryptOnlyPayloadManager).pem.toSend.encrypted)
+			s.Require().Equal(c.PayloadManager.(*MockEncryptOnlyPayloadManager).toSend.plain, s.PS.Received())
+			s.Require().Equal(s.PS.PayloadManager.(*MockEncryptOnlyPayloadManager).received.encrypted, c.PayloadManager.(*MockEncryptOnlyPayloadManager).toSend.encrypted)
 			s.Require().Nil(s.PS.ToSend())
 			s.Require().Nil(c.Received())
 		case Sending:
-			s.Require().Equal(c.Received(), s.PS.PayloadManager.(*MockEncryptOnlyPayloadManager).pem.toSend.plain)
-			s.Require().Equal(c.PayloadManager.(*MockEncryptOnlyPayloadManager).pem.received.encrypted, s.PS.PayloadManager.(*MockEncryptOnlyPayloadManager).pem.toSend.encrypted)
+			s.Require().Equal(c.Received(), s.PS.PayloadManager.(*MockEncryptOnlyPayloadManager).toSend.plain)
+			s.Require().Equal(c.PayloadManager.(*MockEncryptOnlyPayloadManager).received.encrypted, s.PS.PayloadManager.(*MockEncryptOnlyPayloadManager).toSend.encrypted)
 			s.Require().Nil(c.ToSend())
 			s.Require().Nil(s.PS.Received())
 		}
@ -100,3 +101,95 @@ func (s *PairingServerSuite) TestPairingServer_StartPairing() {
 		s.PS.PayloadManager.(*MockEncryptOnlyPayloadManager).ResetPayload()
 	}
 }
+
+func (s *PairingServerSuite) sendingSetup() *PairingClient {
+	// Replace PairingServer.PayloadManager with a MockEncryptOnlyPayloadManager
+	pm, err := NewMockEncryptOnlyPayloadManager(s.EphemeralAES)
+	s.Require().NoError(err)
+	s.PS.PayloadManager = pm
+	s.PS.mode = Sending
+
+	err = s.PS.Mount()
+	s.Require().NoError(err)
+
+	err = s.PS.StartPairing()
+	s.Require().NoError(err)
+
+	// Give time for the sever to be ready, hacky I know, I'll iron this out
+	time.Sleep(10 * time.Millisecond)
+
+	cp, err := s.PS.MakeConnectionParams()
+	s.Require().NoError(err)
+
+	qr := cp.ToString()
+
+	// Client reads QR code and parses the connection string
+	ccp := new(ConnectionParams)
+	err = ccp.FromString(qr)
+	s.Require().NoError(err)
+
+	c, err := NewPairingClient(ccp, nil)
+	s.Require().NoError(err)
+
+	// Replace PairingClient.PayloadManager with a MockEncryptOnlyPayloadManager
+	c.PayloadManager, err = NewMockEncryptOnlyPayloadManager(s.EphemeralAES)
+	s.Require().NoError(err)
+
+	return c
+}
+
+func (s *PairingServerSuite) TestPairingServer_handlePairingChallengeMiddleware() {
+	c := s.sendingSetup()
+
+	// Attempt to get the private key data, this should fail because there is no challenge
+	err := c.receiveAccountData()
+	s.Require().Error(err)
+	s.Require().Equal("status not ok, received '403 Forbidden'", err.Error())
+
+	err = c.getChallenge()
+	s.Require().NoError(err)
+	challenge := c.serverChallenge
+
+	// This is NOT a mistake! Call c.getChallenge() twice to check that the client gets the same challenge
+	// the server will only generate 1 challenge per session per connection
+	err = c.getChallenge()
+	s.Require().NoError(err)
+	s.Require().Equal(challenge, c.serverChallenge)
+
+	// receiving account data should now work.
+	err = c.receiveAccountData()
+	s.Require().NoError(err)
+}
+
+func (s *PairingServerSuite) TestPairingServer_handlePairingChallengeMiddleware_block() {
+	c := s.sendingSetup()
+
+	// Attempt to get the private key data, this should fail because there is no challenge
+	err := c.receiveAccountData()
+	s.Require().Error(err)
+	s.Require().Equal("status not ok, received '403 Forbidden'", err.Error())
+
+	// Get the challenge
+	err = c.getChallenge()
+	s.Require().NoError(err)
+
+	// Simulate encrypting with a dodgy key, write some nonsense to the challenge field
+	c.serverChallenge = make([]byte, 64)
+	_, err = rand.Read(c.serverChallenge)
+	s.Require().NoError(err)
+
+	// Attempt again to get the account data, should fail
+	// behind the scenes the server will block the session if the client fails the challenge. There is no forgiveness!
+	err = c.receiveAccountData()
+	s.Require().Error(err)
+	s.Require().Equal("status not ok, received '403 Forbidden'", err.Error())
+
+	// Get the real challenge
+	err = c.getChallenge()
+	s.Require().NoError(err)
+
+	// Attempt to get the account data, should fail because the client is now blocked.
+	err = c.receiveAccountData()
+	s.Require().Error(err)
+	s.Require().Equal("status not ok, received '403 Forbidden'", err.Error())
+}
--- a/vendor/github.com/gorilla/securecookie/.travis.yml
+++ b/vendor/github.com/gorilla/securecookie/.travis.yml
@ -0,0 +1,19 @@
+language: go
+sudo: false
+
+matrix:
+  include:
+    - go: 1.3
+    - go: 1.4
+    - go: 1.5
+    - go: 1.6
+    - go: 1.7
+    - go: tip
+  allow_failures:
+    - go: tip
+
+script:
+  - go get -t -v ./...
+  - diff -u <(echo -n) <(gofmt -d .)
+  - go vet $(go list ./... | grep -v /vendor/)
+  - go test -v -race ./...
--- a/vendor/github.com/gorilla/securecookie/LICENSE
+++ b/vendor/github.com/gorilla/securecookie/LICENSE
@ -0,0 +1,27 @@
+Copyright (c) 2012 Rodrigo Moraes. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+	 * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+	 * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+	 * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
--- a/vendor/github.com/gorilla/securecookie/README.md
+++ b/vendor/github.com/gorilla/securecookie/README.md
@ -0,0 +1,80 @@
+securecookie
+============
+[![GoDoc](https://godoc.org/github.com/gorilla/securecookie?status.svg)](https://godoc.org/github.com/gorilla/securecookie) [![Build Status](https://travis-ci.org/gorilla/securecookie.png?branch=master)](https://travis-ci.org/gorilla/securecookie)
+[![Sourcegraph](https://sourcegraph.com/github.com/gorilla/securecookie/-/badge.svg)](https://sourcegraph.com/github.com/gorilla/securecookie?badge)
+
+
+securecookie encodes and decodes authenticated and optionally encrypted 
+cookie values.
+
+Secure cookies can't be forged, because their values are validated using HMAC.
+When encrypted, the content is also inaccessible to malicious eyes. It is still
+recommended that sensitive data not be stored in cookies, and that HTTPS be used
+to prevent cookie [replay attacks](https://en.wikipedia.org/wiki/Replay_attack).
+
+## Examples
+
+To use it, first create a new SecureCookie instance:
+
+```go
+// Hash keys should be at least 32 bytes long
+var hashKey = []byte("very-secret")
+// Block keys should be 16 bytes (AES-128) or 32 bytes (AES-256) long.
+// Shorter keys may weaken the encryption used.
+var blockKey = []byte("a-lot-secret")
+var s = securecookie.New(hashKey, blockKey)
+```
+
+The hashKey is required, used to authenticate the cookie value using HMAC.
+It is recommended to use a key with 32 or 64 bytes.
+
+The blockKey is optional, used to encrypt the cookie value -- set it to nil
+to not use encryption. If set, the length must correspond to the block size
+of the encryption algorithm. For AES, used by default, valid lengths are
+16, 24, or 32 bytes to select AES-128, AES-192, or AES-256.
+
+Strong keys can be created using the convenience function GenerateRandomKey().
+
+Once a SecureCookie instance is set, use it to encode a cookie value:
+
+```go
+func SetCookieHandler(w http.ResponseWriter, r *http.Request) {
+	value := map[string]string{
+		"foo": "bar",
+	}
+	if encoded, err := s.Encode("cookie-name", value); err == nil {
+		cookie := &http.Cookie{
+			Name:  "cookie-name",
+			Value: encoded,
+			Path:  "/",
+			Secure: true,
+			HttpOnly: true,
+		}
+		http.SetCookie(w, cookie)
+	}
+}
+```
+
+Later, use the same SecureCookie instance to decode and validate a cookie
+value:
+
+```go
+func ReadCookieHandler(w http.ResponseWriter, r *http.Request) {
+	if cookie, err := r.Cookie("cookie-name"); err == nil {
+		value := make(map[string]string)
+		if err = s2.Decode("cookie-name", cookie.Value, &value); err == nil {
+			fmt.Fprintf(w, "The value of foo is %q", value["foo"])
+		}
+	}
+}
+```
+
+We stored a map[string]string, but secure cookies can hold any value that
+can be encoded using `encoding/gob`. To store custom types, they must be
+registered first using gob.Register(). For basic types this is not needed;
+it works out of the box. An optional JSON encoder that uses `encoding/json` is
+available for types compatible with JSON.
+
+## License
+
+BSD licensed. See the LICENSE file for details.
--- a/vendor/github.com/gorilla/securecookie/doc.go
+++ b/vendor/github.com/gorilla/securecookie/doc.go
@ -0,0 +1,61 @@
+// Copyright 2012 The Gorilla Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+Package securecookie encodes and decodes authenticated and optionally
+encrypted cookie values.
+
+Secure cookies can't be forged, because their values are validated using HMAC.
+When encrypted, the content is also inaccessible to malicious eyes.
+
+To use it, first create a new SecureCookie instance:
+
+	var hashKey = []byte("very-secret")
+	var blockKey = []byte("a-lot-secret")
+	var s = securecookie.New(hashKey, blockKey)
+
+The hashKey is required, used to authenticate the cookie value using HMAC.
+It is recommended to use a key with 32 or 64 bytes.
+
+The blockKey is optional, used to encrypt the cookie value -- set it to nil
+to not use encryption. If set, the length must correspond to the block size
+of the encryption algorithm. For AES, used by default, valid lengths are
+16, 24, or 32 bytes to select AES-128, AES-192, or AES-256.
+
+Strong keys can be created using the convenience function GenerateRandomKey().
+
+Once a SecureCookie instance is set, use it to encode a cookie value:
+
+	func SetCookieHandler(w http.ResponseWriter, r *http.Request) {
+		value := map[string]string{
+			"foo": "bar",
+		}
+		if encoded, err := s.Encode("cookie-name", value); err == nil {
+			cookie := &http.Cookie{
+				Name:  "cookie-name",
+				Value: encoded,
+				Path:  "/",
+			}
+			http.SetCookie(w, cookie)
+		}
+	}
+
+Later, use the same SecureCookie instance to decode and validate a cookie
+value:
+
+	func ReadCookieHandler(w http.ResponseWriter, r *http.Request) {
+		if cookie, err := r.Cookie("cookie-name"); err == nil {
+			value := make(map[string]string)
+			if err = s2.Decode("cookie-name", cookie.Value, &value); err == nil {
+				fmt.Fprintf(w, "The value of foo is %q", value["foo"])
+			}
+		}
+	}
+
+We stored a map[string]string, but secure cookies can hold any value that
+can be encoded using encoding/gob. To store custom types, they must be
+registered first using gob.Register(). For basic types this is not needed;
+it works out of the box.
+*/
+package securecookie
--- a/vendor/github.com/gorilla/securecookie/fuzz.go
+++ b/vendor/github.com/gorilla/securecookie/fuzz.go
@ -0,0 +1,25 @@
+// +build gofuzz
+
+package securecookie
+
+var hashKey = []byte("very-secret12345")
+var blockKey = []byte("a-lot-secret1234")
+var s = New(hashKey, blockKey)
+
+type Cookie struct {
+	B bool
+	I int
+	S string
+}
+
+func Fuzz(data []byte) int {
+	datas := string(data)
+	var c Cookie
+	if err := s.Decode("fuzz", datas, &c); err != nil {
+		return 0
+	}
+	if _, err := s.Encode("fuzz", c); err != nil {
+		panic(err)
+	}
+	return 1
+}
--- a/vendor/github.com/gorilla/securecookie/securecookie.go
+++ b/vendor/github.com/gorilla/securecookie/securecookie.go
@ -0,0 +1,646 @@
+// Copyright 2012 The Gorilla Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package securecookie
+
+import (
+	"bytes"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/hmac"
+	"crypto/rand"
+	"crypto/sha256"
+	"crypto/subtle"
+	"encoding/base64"
+	"encoding/gob"
+	"encoding/json"
+	"fmt"
+	"hash"
+	"io"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Error is the interface of all errors returned by functions in this library.
+type Error interface {
+	error
+
+	// IsUsage returns true for errors indicating the client code probably
+	// uses this library incorrectly.  For example, the client may have
+	// failed to provide a valid hash key, or may have failed to configure
+	// the Serializer adequately for encoding value.
+	IsUsage() bool
+
+	// IsDecode returns true for errors indicating that a cookie could not
+	// be decoded and validated.  Since cookies are usually untrusted
+	// user-provided input, errors of this type should be expected.
+	// Usually, the proper action is simply to reject the request.
+	IsDecode() bool
+
+	// IsInternal returns true for unexpected errors occurring in the
+	// securecookie implementation.
+	IsInternal() bool
+
+	// Cause, if it returns a non-nil value, indicates that this error was
+	// propagated from some underlying library.  If this method returns nil,
+	// this error was raised directly by this library.
+	//
+	// Cause is provided principally for debugging/logging purposes; it is
+	// rare that application logic should perform meaningfully different
+	// logic based on Cause.  See, for example, the caveats described on
+	// (MultiError).Cause().
+	Cause() error
+}
+
+// errorType is a bitmask giving the error type(s) of an cookieError value.
+type errorType int
+
+const (
+	usageError = errorType(1 << iota)
+	decodeError
+	internalError
+)
+
+type cookieError struct {
+	typ   errorType
+	msg   string
+	cause error
+}
+
+func (e cookieError) IsUsage() bool    { return (e.typ & usageError) != 0 }
+func (e cookieError) IsDecode() bool   { return (e.typ & decodeError) != 0 }
+func (e cookieError) IsInternal() bool { return (e.typ & internalError) != 0 }
+
+func (e cookieError) Cause() error { return e.cause }
+
+func (e cookieError) Error() string {
+	parts := []string{"securecookie: "}
+	if e.msg == "" {
+		parts = append(parts, "error")
+	} else {
+		parts = append(parts, e.msg)
+	}
+	if c := e.Cause(); c != nil {
+		parts = append(parts, " - caused by: ", c.Error())
+	}
+	return strings.Join(parts, "")
+}
+
+var (
+	errGeneratingIV = cookieError{typ: internalError, msg: "failed to generate random iv"}
+
+	errNoCodecs            = cookieError{typ: usageError, msg: "no codecs provided"}
+	errHashKeyNotSet       = cookieError{typ: usageError, msg: "hash key is not set"}
+	errBlockKeyNotSet      = cookieError{typ: usageError, msg: "block key is not set"}
+	errEncodedValueTooLong = cookieError{typ: usageError, msg: "the value is too long"}
+
+	errValueToDecodeTooLong = cookieError{typ: decodeError, msg: "the value is too long"}
+	errTimestampInvalid     = cookieError{typ: decodeError, msg: "invalid timestamp"}
+	errTimestampTooNew      = cookieError{typ: decodeError, msg: "timestamp is too new"}
+	errTimestampExpired     = cookieError{typ: decodeError, msg: "expired timestamp"}
+	errDecryptionFailed     = cookieError{typ: decodeError, msg: "the value could not be decrypted"}
+	errValueNotByte         = cookieError{typ: decodeError, msg: "value not a []byte."}
+	errValueNotBytePtr      = cookieError{typ: decodeError, msg: "value not a pointer to []byte."}
+
+	// ErrMacInvalid indicates that cookie decoding failed because the HMAC
+	// could not be extracted and verified.  Direct use of this error
+	// variable is deprecated; it is public only for legacy compatibility,
+	// and may be privatized in the future, as it is rarely useful to
+	// distinguish between this error and other Error implementations.
+	ErrMacInvalid = cookieError{typ: decodeError, msg: "the value is not valid"}
+)
+
+// Codec defines an interface to encode and decode cookie values.
+type Codec interface {
+	Encode(name string, value interface{}) (string, error)
+	Decode(name, value string, dst interface{}) error
+}
+
+// New returns a new SecureCookie.
+//
+// hashKey is required, used to authenticate values using HMAC. Create it using
+// GenerateRandomKey(). It is recommended to use a key with 32 or 64 bytes.
+//
+// blockKey is optional, used to encrypt values. Create it using
+// GenerateRandomKey(). The key length must correspond to the block size
+// of the encryption algorithm. For AES, used by default, valid lengths are
+// 16, 24, or 32 bytes to select AES-128, AES-192, or AES-256.
+// The default encoder used for cookie serialization is encoding/gob.
+//
+// Note that keys created using GenerateRandomKey() are not automatically
+// persisted. New keys will be created when the application is restarted, and
+// previously issued cookies will not be able to be decoded.
+func New(hashKey, blockKey []byte) *SecureCookie {
+	s := &SecureCookie{
+		hashKey:   hashKey,
+		blockKey:  blockKey,
+		hashFunc:  sha256.New,
+		maxAge:    86400 * 30,
+		maxLength: 4096,
+		sz:        GobEncoder{},
+	}
+	if hashKey == nil {
+		s.err = errHashKeyNotSet
+	}
+	if blockKey != nil {
+		s.BlockFunc(aes.NewCipher)
+	}
+	return s
+}
+
+// SecureCookie encodes and decodes authenticated and optionally encrypted
+// cookie values.
+type SecureCookie struct {
+	hashKey   []byte
+	hashFunc  func() hash.Hash
+	blockKey  []byte
+	block     cipher.Block
+	maxLength int
+	maxAge    int64
+	minAge    int64
+	err       error
+	sz        Serializer
+	// For testing purposes, the function that returns the current timestamp.
+	// If not set, it will use time.Now().UTC().Unix().
+	timeFunc func() int64
+}
+
+// Serializer provides an interface for providing custom serializers for cookie
+// values.
+type Serializer interface {
+	Serialize(src interface{}) ([]byte, error)
+	Deserialize(src []byte, dst interface{}) error
+}
+
+// GobEncoder encodes cookie values using encoding/gob. This is the simplest
+// encoder and can handle complex types via gob.Register.
+type GobEncoder struct{}
+
+// JSONEncoder encodes cookie values using encoding/json. Users who wish to
+// encode complex types need to satisfy the json.Marshaller and
+// json.Unmarshaller interfaces.
+type JSONEncoder struct{}
+
+// NopEncoder does not encode cookie values, and instead simply accepts a []byte
+// (as an interface{}) and returns a []byte. This is particularly useful when
+// you encoding an object upstream and do not wish to re-encode it.
+type NopEncoder struct{}
+
+// MaxLength restricts the maximum length, in bytes, for the cookie value.
+//
+// Default is 4096, which is the maximum value accepted by Internet Explorer.
+func (s *SecureCookie) MaxLength(value int) *SecureCookie {
+	s.maxLength = value
+	return s
+}
+
+// MaxAge restricts the maximum age, in seconds, for the cookie value.
+//
+// Default is 86400 * 30. Set it to 0 for no restriction.
+func (s *SecureCookie) MaxAge(value int) *SecureCookie {
+	s.maxAge = int64(value)
+	return s
+}
+
+// MinAge restricts the minimum age, in seconds, for the cookie value.
+//
+// Default is 0 (no restriction).
+func (s *SecureCookie) MinAge(value int) *SecureCookie {
+	s.minAge = int64(value)
+	return s
+}
+
+// HashFunc sets the hash function used to create HMAC.
+//
+// Default is crypto/sha256.New.
+func (s *SecureCookie) HashFunc(f func() hash.Hash) *SecureCookie {
+	s.hashFunc = f
+	return s
+}
+
+// BlockFunc sets the encryption function used to create a cipher.Block.
+//
+// Default is crypto/aes.New.
+func (s *SecureCookie) BlockFunc(f func([]byte) (cipher.Block, error)) *SecureCookie {
+	if s.blockKey == nil {
+		s.err = errBlockKeyNotSet
+	} else if block, err := f(s.blockKey); err == nil {
+		s.block = block
+	} else {
+		s.err = cookieError{cause: err, typ: usageError}
+	}
+	return s
+}
+
+// Encoding sets the encoding/serialization method for cookies.
+//
+// Default is encoding/gob.  To encode special structures using encoding/gob,
+// they must be registered first using gob.Register().
+func (s *SecureCookie) SetSerializer(sz Serializer) *SecureCookie {
+	s.sz = sz
+
+	return s
+}
+
+// Encode encodes a cookie value.
+//
+// It serializes, optionally encrypts, signs with a message authentication code,
+// and finally encodes the value.
+//
+// The name argument is the cookie name. It is stored with the encoded value.
+// The value argument is the value to be encoded. It can be any value that can
+// be encoded using the currently selected serializer; see SetSerializer().
+//
+// It is the client's responsibility to ensure that value, when encoded using
+// the current serialization/encryption settings on s and then base64-encoded,
+// is shorter than the maximum permissible length.
+func (s *SecureCookie) Encode(name string, value interface{}) (string, error) {
+	if s.err != nil {
+		return "", s.err
+	}
+	if s.hashKey == nil {
+		s.err = errHashKeyNotSet
+		return "", s.err
+	}
+	var err error
+	var b []byte
+	// 1. Serialize.
+	if b, err = s.sz.Serialize(value); err != nil {
+		return "", cookieError{cause: err, typ: usageError}
+	}
+	// 2. Encrypt (optional).
+	if s.block != nil {
+		if b, err = encrypt(s.block, b); err != nil {
+			return "", cookieError{cause: err, typ: usageError}
+		}
+	}
+	b = encode(b)
+	// 3. Create MAC for "name|date|value". Extra pipe to be used later.
+	b = []byte(fmt.Sprintf("%s|%d|%s|", name, s.timestamp(), b))
+	mac := createMac(hmac.New(s.hashFunc, s.hashKey), b[:len(b)-1])
+	// Append mac, remove name.
+	b = append(b, mac...)[len(name)+1:]
+	// 4. Encode to base64.
+	b = encode(b)
+	// 5. Check length.
+	if s.maxLength != 0 && len(b) > s.maxLength {
+		return "", errEncodedValueTooLong
+	}
+	// Done.
+	return string(b), nil
+}
+
+// Decode decodes a cookie value.
+//
+// It decodes, verifies a message authentication code, optionally decrypts and
+// finally deserializes the value.
+//
+// The name argument is the cookie name. It must be the same name used when
+// it was stored. The value argument is the encoded cookie value. The dst
+// argument is where the cookie will be decoded. It must be a pointer.
+func (s *SecureCookie) Decode(name, value string, dst interface{}) error {
+	if s.err != nil {
+		return s.err
+	}
+	if s.hashKey == nil {
+		s.err = errHashKeyNotSet
+		return s.err
+	}
+	// 1. Check length.
+	if s.maxLength != 0 && len(value) > s.maxLength {
+		return errValueToDecodeTooLong
+	}
+	// 2. Decode from base64.
+	b, err := decode([]byte(value))
+	if err != nil {
+		return err
+	}
+	// 3. Verify MAC. Value is "date|value|mac".
+	parts := bytes.SplitN(b, []byte("|"), 3)
+	if len(parts) != 3 {
+		return ErrMacInvalid
+	}
+	h := hmac.New(s.hashFunc, s.hashKey)
+	b = append([]byte(name+"|"), b[:len(b)-len(parts[2])-1]...)
+	if err = verifyMac(h, b, parts[2]); err != nil {
+		return err
+	}
+	// 4. Verify date ranges.
+	var t1 int64
+	if t1, err = strconv.ParseInt(string(parts[0]), 10, 64); err != nil {
+		return errTimestampInvalid
+	}
+	t2 := s.timestamp()
+	if s.minAge != 0 && t1 > t2-s.minAge {
+		return errTimestampTooNew
+	}
+	if s.maxAge != 0 && t1 < t2-s.maxAge {
+		return errTimestampExpired
+	}
+	// 5. Decrypt (optional).
+	b, err = decode(parts[1])
+	if err != nil {
+		return err
+	}
+	if s.block != nil {
+		if b, err = decrypt(s.block, b); err != nil {
+			return err
+		}
+	}
+	// 6. Deserialize.
+	if err = s.sz.Deserialize(b, dst); err != nil {
+		return cookieError{cause: err, typ: decodeError}
+	}
+	// Done.
+	return nil
+}
+
+// timestamp returns the current timestamp, in seconds.
+//
+// For testing purposes, the function that generates the timestamp can be
+// overridden. If not set, it will return time.Now().UTC().Unix().
+func (s *SecureCookie) timestamp() int64 {
+	if s.timeFunc == nil {
+		return time.Now().UTC().Unix()
+	}
+	return s.timeFunc()
+}
+
+// Authentication -------------------------------------------------------------
+
+// createMac creates a message authentication code (MAC).
+func createMac(h hash.Hash, value []byte) []byte {
+	h.Write(value)
+	return h.Sum(nil)
+}
+
+// verifyMac verifies that a message authentication code (MAC) is valid.
+func verifyMac(h hash.Hash, value []byte, mac []byte) error {
+	mac2 := createMac(h, value)
+	// Check that both MACs are of equal length, as subtle.ConstantTimeCompare
+	// does not do this prior to Go 1.4.
+	if len(mac) == len(mac2) && subtle.ConstantTimeCompare(mac, mac2) == 1 {
+		return nil
+	}
+	return ErrMacInvalid
+}
+
+// Encryption -----------------------------------------------------------------
+
+// encrypt encrypts a value using the given block in counter mode.
+//
+// A random initialization vector (http://goo.gl/zF67k) with the length of the
+// block size is prepended to the resulting ciphertext.
+func encrypt(block cipher.Block, value []byte) ([]byte, error) {
+	iv := GenerateRandomKey(block.BlockSize())
+	if iv == nil {
+		return nil, errGeneratingIV
+	}
+	// Encrypt it.
+	stream := cipher.NewCTR(block, iv)
+	stream.XORKeyStream(value, value)
+	// Return iv + ciphertext.
+	return append(iv, value...), nil
+}
+
+// decrypt decrypts a value using the given block in counter mode.
+//
+// The value to be decrypted must be prepended by a initialization vector
+// (http://goo.gl/zF67k) with the length of the block size.
+func decrypt(block cipher.Block, value []byte) ([]byte, error) {
+	size := block.BlockSize()
+	if len(value) > size {
+		// Extract iv.
+		iv := value[:size]
+		// Extract ciphertext.
+		value = value[size:]
+		// Decrypt it.
+		stream := cipher.NewCTR(block, iv)
+		stream.XORKeyStream(value, value)
+		return value, nil
+	}
+	return nil, errDecryptionFailed
+}
+
+// Serialization --------------------------------------------------------------
+
+// Serialize encodes a value using gob.
+func (e GobEncoder) Serialize(src interface{}) ([]byte, error) {
+	buf := new(bytes.Buffer)
+	enc := gob.NewEncoder(buf)
+	if err := enc.Encode(src); err != nil {
+		return nil, cookieError{cause: err, typ: usageError}
+	}
+	return buf.Bytes(), nil
+}
+
+// Deserialize decodes a value using gob.
+func (e GobEncoder) Deserialize(src []byte, dst interface{}) error {
+	dec := gob.NewDecoder(bytes.NewBuffer(src))
+	if err := dec.Decode(dst); err != nil {
+		return cookieError{cause: err, typ: decodeError}
+	}
+	return nil
+}
+
+// Serialize encodes a value using encoding/json.
+func (e JSONEncoder) Serialize(src interface{}) ([]byte, error) {
+	buf := new(bytes.Buffer)
+	enc := json.NewEncoder(buf)
+	if err := enc.Encode(src); err != nil {
+		return nil, cookieError{cause: err, typ: usageError}
+	}
+	return buf.Bytes(), nil
+}
+
+// Deserialize decodes a value using encoding/json.
+func (e JSONEncoder) Deserialize(src []byte, dst interface{}) error {
+	dec := json.NewDecoder(bytes.NewReader(src))
+	if err := dec.Decode(dst); err != nil {
+		return cookieError{cause: err, typ: decodeError}
+	}
+	return nil
+}
+
+// Serialize passes a []byte through as-is.
+func (e NopEncoder) Serialize(src interface{}) ([]byte, error) {
+	if b, ok := src.([]byte); ok {
+		return b, nil
+	}
+
+	return nil, errValueNotByte
+}
+
+// Deserialize passes a []byte through as-is.
+func (e NopEncoder) Deserialize(src []byte, dst interface{}) error {
+	if dat, ok := dst.(*[]byte); ok {
+		*dat = src
+		return nil
+	}
+	return errValueNotBytePtr
+}
+
+// Encoding -------------------------------------------------------------------
+
+// encode encodes a value using base64.
+func encode(value []byte) []byte {
+	encoded := make([]byte, base64.URLEncoding.EncodedLen(len(value)))
+	base64.URLEncoding.Encode(encoded, value)
+	return encoded
+}
+
+// decode decodes a cookie using base64.
+func decode(value []byte) ([]byte, error) {
+	decoded := make([]byte, base64.URLEncoding.DecodedLen(len(value)))
+	b, err := base64.URLEncoding.Decode(decoded, value)
+	if err != nil {
+		return nil, cookieError{cause: err, typ: decodeError, msg: "base64 decode failed"}
+	}
+	return decoded[:b], nil
+}
+
+// Helpers --------------------------------------------------------------------
+
+// GenerateRandomKey creates a random key with the given length in bytes.
+// On failure, returns nil.
+//
+// Callers should explicitly check for the possibility of a nil return, treat
+// it as a failure of the system random number generator, and not continue.
+func GenerateRandomKey(length int) []byte {
+	k := make([]byte, length)
+	if _, err := io.ReadFull(rand.Reader, k); err != nil {
+		return nil
+	}
+	return k
+}
+
+// CodecsFromPairs returns a slice of SecureCookie instances.
+//
+// It is a convenience function to create a list of codecs for key rotation. Note
+// that the generated Codecs will have the default options applied: callers
+// should iterate over each Codec and type-assert the underlying *SecureCookie to
+// change these.
+//
+// Example:
+//
+//      codecs := securecookie.CodecsFromPairs(
+//           []byte("new-hash-key"),
+//           []byte("new-block-key"),
+//           []byte("old-hash-key"),
+//           []byte("old-block-key"),
+//       )
+//
+//      // Modify each instance.
+//      for _, s := range codecs {
+//             if cookie, ok := s.(*securecookie.SecureCookie); ok {
+//                 cookie.MaxAge(86400 * 7)
+//                 cookie.SetSerializer(securecookie.JSONEncoder{})
+//                 cookie.HashFunc(sha512.New512_256)
+//             }
+//         }
+//
+func CodecsFromPairs(keyPairs ...[]byte) []Codec {
+	codecs := make([]Codec, len(keyPairs)/2+len(keyPairs)%2)
+	for i := 0; i < len(keyPairs); i += 2 {
+		var blockKey []byte
+		if i+1 < len(keyPairs) {
+			blockKey = keyPairs[i+1]
+		}
+		codecs[i/2] = New(keyPairs[i], blockKey)
+	}
+	return codecs
+}
+
+// EncodeMulti encodes a cookie value using a group of codecs.
+//
+// The codecs are tried in order. Multiple codecs are accepted to allow
+// key rotation.
+//
+// On error, may return a MultiError.
+func EncodeMulti(name string, value interface{}, codecs ...Codec) (string, error) {
+	if len(codecs) == 0 {
+		return "", errNoCodecs
+	}
+
+	var errors MultiError
+	for _, codec := range codecs {
+		encoded, err := codec.Encode(name, value)
+		if err == nil {
+			return encoded, nil
+		}
+		errors = append(errors, err)
+	}
+	return "", errors
+}
+
+// DecodeMulti decodes a cookie value using a group of codecs.
+//
+// The codecs are tried in order. Multiple codecs are accepted to allow
+// key rotation.
+//
+// On error, may return a MultiError.
+func DecodeMulti(name string, value string, dst interface{}, codecs ...Codec) error {
+	if len(codecs) == 0 {
+		return errNoCodecs
+	}
+
+	var errors MultiError
+	for _, codec := range codecs {
+		err := codec.Decode(name, value, dst)
+		if err == nil {
+			return nil
+		}
+		errors = append(errors, err)
+	}
+	return errors
+}
+
+// MultiError groups multiple errors.
+type MultiError []error
+
+func (m MultiError) IsUsage() bool    { return m.any(func(e Error) bool { return e.IsUsage() }) }
+func (m MultiError) IsDecode() bool   { return m.any(func(e Error) bool { return e.IsDecode() }) }
+func (m MultiError) IsInternal() bool { return m.any(func(e Error) bool { return e.IsInternal() }) }
+
+// Cause returns nil for MultiError; there is no unique underlying cause in the
+// general case.
+//
+// Note: we could conceivably return a non-nil Cause only when there is exactly
+// one child error with a Cause.  However, it would be brittle for client code
+// to rely on the arity of causes inside a MultiError, so we have opted not to
+// provide this functionality.  Clients which really wish to access the Causes
+// of the underlying errors are free to iterate through the errors themselves.
+func (m MultiError) Cause() error { return nil }
+
+func (m MultiError) Error() string {
+	s, n := "", 0
+	for _, e := range m {
+		if e != nil {
+			if n == 0 {
+				s = e.Error()
+			}
+			n++
+		}
+	}
+	switch n {
+	case 0:
+		return "(0 errors)"
+	case 1:
+		return s
+	case 2:
+		return s + " (and 1 other error)"
+	}
+	return fmt.Sprintf("%s (and %d other errors)", s, n-1)
+}
+
+// any returns true if any element of m is an Error for which pred returns true.
+func (m MultiError) any(pred func(Error) bool) bool {
+	for _, e := range m {
+		if ourErr, ok := e.(Error); ok && pred(ourErr) {
+			return true
+		}
+	}
+	return false
+}
--- a/vendor/github.com/gorilla/sessions/AUTHORS
+++ b/vendor/github.com/gorilla/sessions/AUTHORS
@ -0,0 +1,43 @@
+# This is the official list of gorilla/sessions authors for copyright purposes.
+#
+# Please keep the list sorted.
+
+Ahmadreza Zibaei <ahmadrezazibaei@hotmail.com>
+Anton Lindström <lindztr@gmail.com>
+Brian Jones <mojobojo@gmail.com>
+Collin Stedman <kronion@users.noreply.github.com>
+Deniz Eren <dee.116@gmail.com>
+Dmitry Chestnykh <dmitry@codingrobots.com>
+Dustin Oprea <myselfasunder@gmail.com>
+Egon Elbre <egonelbre@gmail.com>
+enumappstore <appstore@enumapps.com>
+Geofrey Ernest <geofreyernest@live.com>
+Google LLC (https://opensource.google.com/)
+Jerry Saravia <SaraviaJ@gmail.com>
+Jonathan Gillham <jonathan.gillham@gamil.com>
+Justin Clift <justin@postgresql.org>
+Justin Hellings <justin.hellings@gmail.com>
+Kamil Kisiel <kamil@kamilkisiel.net>
+Keiji Yoshida <yoshida.keiji.84@gmail.com>
+kliron <kliron@gmail.com>
+Kshitij Saraogi <KshitijSaraogi@gmail.com>
+Lauris BH <lauris@nix.lv>
+Lukas Rist <glaslos@gmail.com>
+Mark Dain <ancarda@users.noreply.github.com>
+Matt Ho <matt.ho@gmail.com>
+Matt Silverlock <matt@eatsleeprepeat.net>
+Mattias Wadman <mattias.wadman@gmail.com>
+Michael Schuett <michaeljs1990@gmail.com>
+Michael Stapelberg <stapelberg@users.noreply.github.com>
+Mirco Zeiss <mirco.zeiss@gmail.com>
+moraes <rodrigo.moraes@gmail.com>
+nvcnvn <nguyen@open-vn.org>
+pappz <zoltan.pmail@gmail.com>
+Pontus Leitzler <leitzler@users.noreply.github.com>
+QuaSoft <info@quasoft.net>
+rcadena <robert.cadena@gmail.com>
+rodrigo moraes <rodrigo.moraes@gmail.com>
+Shawn Smith <shawnpsmith@gmail.com>
+Taylor Hurt <taylor.a.hurt@gmail.com>
+Tortuoise <sanyasinp@gmail.com>
+Vitor De Mario <vitordemario@gmail.com>
--- a/vendor/github.com/gorilla/sessions/LICENSE
+++ b/vendor/github.com/gorilla/sessions/LICENSE
@ -0,0 +1,27 @@
+Copyright (c) 2012-2018 The Gorilla Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+	 * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+	 * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+	 * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
--- a/vendor/github.com/gorilla/sessions/README.md
+++ b/vendor/github.com/gorilla/sessions/README.md
@ -0,0 +1,90 @@
+# sessions
+
+[![GoDoc](https://godoc.org/github.com/gorilla/sessions?status.svg)](https://godoc.org/github.com/gorilla/sessions) [![Build Status](https://travis-ci.org/gorilla/sessions.svg?branch=master)](https://travis-ci.org/gorilla/sessions)
+[![Sourcegraph](https://sourcegraph.com/github.com/gorilla/sessions/-/badge.svg)](https://sourcegraph.com/github.com/gorilla/sessions?badge)
+
+gorilla/sessions provides cookie and filesystem sessions and infrastructure for
+custom session backends.
+
+The key features are:
+
+- Simple API: use it as an easy way to set signed (and optionally
+  encrypted) cookies.
+- Built-in backends to store sessions in cookies or the filesystem.
+- Flash messages: session values that last until read.
+- Convenient way to switch session persistency (aka "remember me") and set
+  other attributes.
+- Mechanism to rotate authentication and encryption keys.
+- Multiple sessions per request, even using different backends.
+- Interfaces and infrastructure for custom session backends: sessions from
+  different stores can be retrieved and batch-saved using a common API.
+
+Let's start with an example that shows the sessions API in a nutshell:
+
+```go
+	import (
+		"net/http"
+		"github.com/gorilla/sessions"
+	)
+
+	// Note: Don't store your key in your source code. Pass it via an
+	// environmental variable, or flag (or both), and don't accidentally commit it
+	// alongside your code. Ensure your key is sufficiently random - i.e. use Go's
+	// crypto/rand or securecookie.GenerateRandomKey(32) and persist the result.
+	var store = sessions.NewCookieStore([]byte(os.Getenv("SESSION_KEY")))
+
+	func MyHandler(w http.ResponseWriter, r *http.Request) {
+		// Get a session. We're ignoring the error resulted from decoding an
+		// existing session: Get() always returns a session, even if empty.
+		session, _ := store.Get(r, "session-name")
+		// Set some session values.
+		session.Values["foo"] = "bar"
+		session.Values[42] = 43
+		// Save it before we write to the response/return from the handler.
+		err := session.Save(r, w)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+	}
+```
+
+First we initialize a session store calling `NewCookieStore()` and passing a
+secret key used to authenticate the session. Inside the handler, we call
+`store.Get()` to retrieve an existing session or create a new one. Then we set
+some session values in session.Values, which is a `map[interface{}]interface{}`.
+And finally we call `session.Save()` to save the session in the response.
+
+More examples are available [on the Gorilla
+website](https://www.gorillatoolkit.org/pkg/sessions).
+
+## Store Implementations
+
+Other implementations of the `sessions.Store` interface:
+
+- [github.com/starJammer/gorilla-sessions-arangodb](https://github.com/starJammer/gorilla-sessions-arangodb) - ArangoDB
+- [github.com/yosssi/boltstore](https://github.com/yosssi/boltstore) - Bolt
+- [github.com/srinathgs/couchbasestore](https://github.com/srinathgs/couchbasestore) - Couchbase
+- [github.com/denizeren/dynamostore](https://github.com/denizeren/dynamostore) - Dynamodb on AWS
+- [github.com/savaki/dynastore](https://github.com/savaki/dynastore) - DynamoDB on AWS (Official AWS library)
+- [github.com/bradleypeabody/gorilla-sessions-memcache](https://github.com/bradleypeabody/gorilla-sessions-memcache) - Memcache
+- [github.com/dsoprea/go-appengine-sessioncascade](https://github.com/dsoprea/go-appengine-sessioncascade) - Memcache/Datastore/Context in AppEngine
+- [github.com/kidstuff/mongostore](https://github.com/kidstuff/mongostore) - MongoDB
+- [github.com/srinathgs/mysqlstore](https://github.com/srinathgs/mysqlstore) - MySQL
+- [github.com/EnumApps/clustersqlstore](https://github.com/EnumApps/clustersqlstore) - MySQL Cluster
+- [github.com/antonlindstrom/pgstore](https://github.com/antonlindstrom/pgstore) - PostgreSQL
+- [github.com/boj/redistore](https://github.com/boj/redistore) - Redis
+- [github.com/rbcervilla/redisstore](https://github.com/rbcervilla/redisstore) - Redis (Single, Sentinel, Cluster)
+- [github.com/boj/rethinkstore](https://github.com/boj/rethinkstore) - RethinkDB
+- [github.com/boj/riakstore](https://github.com/boj/riakstore) - Riak
+- [github.com/michaeljs1990/sqlitestore](https://github.com/michaeljs1990/sqlitestore) - SQLite
+- [github.com/wader/gormstore](https://github.com/wader/gormstore) - GORM (MySQL, PostgreSQL, SQLite)
+- [github.com/gernest/qlstore](https://github.com/gernest/qlstore) - ql
+- [github.com/quasoft/memstore](https://github.com/quasoft/memstore) - In-memory implementation for use in unit tests
+- [github.com/lafriks/xormstore](https://github.com/lafriks/xormstore) - XORM (MySQL, PostgreSQL, SQLite, Microsoft SQL Server, TiDB)
+- [github.com/GoogleCloudPlatform/firestore-gorilla-sessions](https://github.com/GoogleCloudPlatform/firestore-gorilla-sessions) - Cloud Firestore
+- [github.com/stephenafamo/crdbstore](https://github.com/stephenafamo/crdbstore) - CockroachDB
+
+## License
+
+BSD licensed. See the LICENSE file for details.
--- a/vendor/github.com/gorilla/sessions/cookie.go
+++ b/vendor/github.com/gorilla/sessions/cookie.go
@ -0,0 +1,19 @@
+// +build !go1.11
+
+package sessions
+
+import "net/http"
+
+// newCookieFromOptions returns an http.Cookie with the options set.
+func newCookieFromOptions(name, value string, options *Options) *http.Cookie {
+	return &http.Cookie{
+		Name:     name,
+		Value:    value,
+		Path:     options.Path,
+		Domain:   options.Domain,
+		MaxAge:   options.MaxAge,
+		Secure:   options.Secure,
+		HttpOnly: options.HttpOnly,
+	}
+
+}
--- a/vendor/github.com/gorilla/sessions/cookie_go111.go
+++ b/vendor/github.com/gorilla/sessions/cookie_go111.go
@ -0,0 +1,20 @@
+// +build go1.11
+
+package sessions
+
+import "net/http"
+
+// newCookieFromOptions returns an http.Cookie with the options set.
+func newCookieFromOptions(name, value string, options *Options) *http.Cookie {
+	return &http.Cookie{
+		Name:     name,
+		Value:    value,
+		Path:     options.Path,
+		Domain:   options.Domain,
+		MaxAge:   options.MaxAge,
+		Secure:   options.Secure,
+		HttpOnly: options.HttpOnly,
+		SameSite: options.SameSite,
+	}
+
+}
--- a/vendor/github.com/gorilla/sessions/doc.go
+++ b/vendor/github.com/gorilla/sessions/doc.go
@ -0,0 +1,207 @@
+// Copyright 2012 The Gorilla Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+Package sessions provides cookie and filesystem sessions and
+infrastructure for custom session backends.
+
+The key features are:
+
+	* Simple API: use it as an easy way to set signed (and optionally
+	  encrypted) cookies.
+	* Built-in backends to store sessions in cookies or the filesystem.
+	* Flash messages: session values that last until read.
+	* Convenient way to switch session persistency (aka "remember me") and set
+	  other attributes.
+	* Mechanism to rotate authentication and encryption keys.
+	* Multiple sessions per request, even using different backends.
+	* Interfaces and infrastructure for custom session backends: sessions from
+	  different stores can be retrieved and batch-saved using a common API.
+
+Let's start with an example that shows the sessions API in a nutshell:
+
+	import (
+		"net/http"
+		"github.com/gorilla/sessions"
+	)
+
+	// Note: Don't store your key in your source code. Pass it via an
+	// environmental variable, or flag (or both), and don't accidentally commit it
+	// alongside your code. Ensure your key is sufficiently random - i.e. use Go's
+	// crypto/rand or securecookie.GenerateRandomKey(32) and persist the result.
+	// Ensure SESSION_KEY exists in the environment, or sessions will fail.
+	var store = sessions.NewCookieStore([]byte(os.Getenv("SESSION_KEY")))
+
+	func MyHandler(w http.ResponseWriter, r *http.Request) {
+		// Get a session. Get() always returns a session, even if empty.
+		session, err := store.Get(r, "session-name")
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+
+		// Set some session values.
+		session.Values["foo"] = "bar"
+		session.Values[42] = 43
+		// Save it before we write to the response/return from the handler.
+		err = session.Save(r, w)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+	}
+
+First we initialize a session store calling NewCookieStore() and passing a
+secret key used to authenticate the session. Inside the handler, we call
+store.Get() to retrieve an existing session or a new one. Then we set some
+session values in session.Values, which is a map[interface{}]interface{}.
+And finally we call session.Save() to save the session in the response.
+
+Note that in production code, we should check for errors when calling
+session.Save(r, w), and either display an error message or otherwise handle it.
+
+Save must be called before writing to the response, otherwise the session
+cookie will not be sent to the client.
+
+That's all you need to know for the basic usage. Let's take a look at other
+options, starting with flash messages.
+
+Flash messages are session values that last until read. The term appeared with
+Ruby On Rails a few years back. When we request a flash message, it is removed
+from the session. To add a flash, call session.AddFlash(), and to get all
+flashes, call session.Flashes(). Here is an example:
+
+	func MyHandler(w http.ResponseWriter, r *http.Request) {
+		// Get a session.
+		session, err := store.Get(r, "session-name")
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+
+		// Get the previous flashes, if any.
+		if flashes := session.Flashes(); len(flashes) > 0 {
+			// Use the flash values.
+		} else {
+			// Set a new flash.
+			session.AddFlash("Hello, flash messages world!")
+		}
+		err = session.Save(r, w)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+	}
+
+Flash messages are useful to set information to be read after a redirection,
+like after form submissions.
+
+There may also be cases where you want to store a complex datatype within a
+session, such as a struct. Sessions are serialised using the encoding/gob package,
+so it is easy to register new datatypes for storage in sessions:
+
+	import(
+		"encoding/gob"
+		"github.com/gorilla/sessions"
+	)
+
+	type Person struct {
+		FirstName	string
+		LastName 	string
+		Email		string
+		Age			int
+	}
+
+	type M map[string]interface{}
+
+	func init() {
+
+		gob.Register(&Person{})
+		gob.Register(&M{})
+	}
+
+As it's not possible to pass a raw type as a parameter to a function, gob.Register()
+relies on us passing it a value of the desired type. In the example above we've passed
+it a pointer to a struct and a pointer to a custom type representing a
+map[string]interface. (We could have passed non-pointer values if we wished.) This will
+then allow us to serialise/deserialise values of those types to and from our sessions.
+
+Note that because session values are stored in a map[string]interface{}, there's
+a need to type-assert data when retrieving it. We'll use the Person struct we registered above:
+
+	func MyHandler(w http.ResponseWriter, r *http.Request) {
+		session, err := store.Get(r, "session-name")
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+
+		// Retrieve our struct and type-assert it
+		val := session.Values["person"]
+		var person = &Person{}
+		if person, ok := val.(*Person); !ok {
+			// Handle the case that it's not an expected type
+		}
+
+		// Now we can use our person object
+	}
+
+By default, session cookies last for a month. This is probably too long for
+some cases, but it is easy to change this and other attributes during
+runtime. Sessions can be configured individually or the store can be
+configured and then all sessions saved using it will use that configuration.
+We access session.Options or store.Options to set a new configuration. The
+fields are basically a subset of http.Cookie fields. Let's change the
+maximum age of a session to one week:
+
+	session.Options = &sessions.Options{
+		Path:     "/",
+		MaxAge:   86400 * 7,
+		HttpOnly: true,
+	}
+
+Sometimes we may want to change authentication and/or encryption keys without
+breaking existing sessions. The CookieStore supports key rotation, and to use
+it you just need to set multiple authentication and encryption keys, in pairs,
+to be tested in order:
+
+	var store = sessions.NewCookieStore(
+		[]byte("new-authentication-key"),
+		[]byte("new-encryption-key"),
+		[]byte("old-authentication-key"),
+		[]byte("old-encryption-key"),
+	)
+
+New sessions will be saved using the first pair. Old sessions can still be
+read because the first pair will fail, and the second will be tested. This
+makes it easy to "rotate" secret keys and still be able to validate existing
+sessions. Note: for all pairs the encryption key is optional; set it to nil
+or omit it and and encryption won't be used.
+
+Multiple sessions can be used in the same request, even with different
+session backends. When this happens, calling Save() on each session
+individually would be cumbersome, so we have a way to save all sessions
+at once: it's sessions.Save(). Here's an example:
+
+	var store = sessions.NewCookieStore([]byte("something-very-secret"))
+
+	func MyHandler(w http.ResponseWriter, r *http.Request) {
+		// Get a session and set a value.
+		session1, _ := store.Get(r, "session-one")
+		session1.Values["foo"] = "bar"
+		// Get another session and set another value.
+		session2, _ := store.Get(r, "session-two")
+		session2.Values[42] = 43
+		// Save all sessions.
+		err = sessions.Save(r, w)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+	}
+
+This is possible because when we call Get() from a session store, it adds the
+session to a common registry. Save() uses it to save all registered sessions.
+*/
+package sessions
--- a/vendor/github.com/gorilla/sessions/lex.go
+++ b/vendor/github.com/gorilla/sessions/lex.go
@ -0,0 +1,102 @@
+// This file contains code adapted from the Go standard library
+// https://github.com/golang/go/blob/39ad0fd0789872f9469167be7fe9578625ff246e/src/net/http/lex.go
+
+package sessions
+
+import "strings"
+
+var isTokenTable = [127]bool{
+	'!':  true,
+	'#':  true,
+	'$':  true,
+	'%':  true,
+	'&':  true,
+	'\'': true,
+	'*':  true,
+	'+':  true,
+	'-':  true,
+	'.':  true,
+	'0':  true,
+	'1':  true,
+	'2':  true,
+	'3':  true,
+	'4':  true,
+	'5':  true,
+	'6':  true,
+	'7':  true,
+	'8':  true,
+	'9':  true,
+	'A':  true,
+	'B':  true,
+	'C':  true,
+	'D':  true,
+	'E':  true,
+	'F':  true,
+	'G':  true,
+	'H':  true,
+	'I':  true,
+	'J':  true,
+	'K':  true,
+	'L':  true,
+	'M':  true,
+	'N':  true,
+	'O':  true,
+	'P':  true,
+	'Q':  true,
+	'R':  true,
+	'S':  true,
+	'T':  true,
+	'U':  true,
+	'W':  true,
+	'V':  true,
+	'X':  true,
+	'Y':  true,
+	'Z':  true,
+	'^':  true,
+	'_':  true,
+	'`':  true,
+	'a':  true,
+	'b':  true,
+	'c':  true,
+	'd':  true,
+	'e':  true,
+	'f':  true,
+	'g':  true,
+	'h':  true,
+	'i':  true,
+	'j':  true,
+	'k':  true,
+	'l':  true,
+	'm':  true,
+	'n':  true,
+	'o':  true,
+	'p':  true,
+	'q':  true,
+	'r':  true,
+	's':  true,
+	't':  true,
+	'u':  true,
+	'v':  true,
+	'w':  true,
+	'x':  true,
+	'y':  true,
+	'z':  true,
+	'|':  true,
+	'~':  true,
+}
+
+func isToken(r rune) bool {
+	i := int(r)
+	return i < len(isTokenTable) && isTokenTable[i]
+}
+
+func isNotToken(r rune) bool {
+	return !isToken(r)
+}
+
+func isCookieNameValid(raw string) bool {
+	if raw == "" {
+		return false
+	}
+	return strings.IndexFunc(raw, isNotToken) < 0
+}
--- a/vendor/github.com/gorilla/sessions/options.go
+++ b/vendor/github.com/gorilla/sessions/options.go
@ -0,0 +1,18 @@
+// +build !go1.11
+
+package sessions
+
+// Options stores configuration for a session or session store.
+//
+// Fields are a subset of http.Cookie fields.
+type Options struct {
+	Path   string
+	Domain string
+	// MaxAge=0 means no Max-Age attribute specified and the cookie will be
+	// deleted after the browser session ends.
+	// MaxAge<0 means delete cookie immediately.
+	// MaxAge>0 means Max-Age attribute present and given in seconds.
+	MaxAge   int
+	Secure   bool
+	HttpOnly bool
+}
--- a/vendor/github.com/gorilla/sessions/options_go111.go
+++ b/vendor/github.com/gorilla/sessions/options_go111.go
@ -0,0 +1,22 @@
+// +build go1.11
+
+package sessions
+
+import "net/http"
+
+// Options stores configuration for a session or session store.
+//
+// Fields are a subset of http.Cookie fields.
+type Options struct {
+	Path   string
+	Domain string
+	// MaxAge=0 means no Max-Age attribute specified and the cookie will be
+	// deleted after the browser session ends.
+	// MaxAge<0 means delete cookie immediately.
+	// MaxAge>0 means Max-Age attribute present and given in seconds.
+	MaxAge   int
+	Secure   bool
+	HttpOnly bool
+	// Defaults to http.SameSiteDefaultMode
+	SameSite http.SameSite
+}
--- a/vendor/github.com/gorilla/sessions/sessions.go
+++ b/vendor/github.com/gorilla/sessions/sessions.go
@ -0,0 +1,218 @@
+// Copyright 2012 The Gorilla Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sessions
+
+import (
+	"context"
+	"encoding/gob"
+	"fmt"
+	"net/http"
+	"time"
+)
+
+// Default flashes key.
+const flashesKey = "_flash"
+
+// Session --------------------------------------------------------------------
+
+// NewSession is called by session stores to create a new session instance.
+func NewSession(store Store, name string) *Session {
+	return &Session{
+		Values:  make(map[interface{}]interface{}),
+		store:   store,
+		name:    name,
+		Options: new(Options),
+	}
+}
+
+// Session stores the values and optional configuration for a session.
+type Session struct {
+	// The ID of the session, generated by stores. It should not be used for
+	// user data.
+	ID string
+	// Values contains the user-data for the session.
+	Values  map[interface{}]interface{}
+	Options *Options
+	IsNew   bool
+	store   Store
+	name    string
+}
+
+// Flashes returns a slice of flash messages from the session.
+//
+// A single variadic argument is accepted, and it is optional: it defines
+// the flash key. If not defined "_flash" is used by default.
+func (s *Session) Flashes(vars ...string) []interface{} {
+	var flashes []interface{}
+	key := flashesKey
+	if len(vars) > 0 {
+		key = vars[0]
+	}
+	if v, ok := s.Values[key]; ok {
+		// Drop the flashes and return it.
+		delete(s.Values, key)
+		flashes = v.([]interface{})
+	}
+	return flashes
+}
+
+// AddFlash adds a flash message to the session.
+//
+// A single variadic argument is accepted, and it is optional: it defines
+// the flash key. If not defined "_flash" is used by default.
+func (s *Session) AddFlash(value interface{}, vars ...string) {
+	key := flashesKey
+	if len(vars) > 0 {
+		key = vars[0]
+	}
+	var flashes []interface{}
+	if v, ok := s.Values[key]; ok {
+		flashes = v.([]interface{})
+	}
+	s.Values[key] = append(flashes, value)
+}
+
+// Save is a convenience method to save this session. It is the same as calling
+// store.Save(request, response, session). You should call Save before writing to
+// the response or returning from the handler.
+func (s *Session) Save(r *http.Request, w http.ResponseWriter) error {
+	return s.store.Save(r, w, s)
+}
+
+// Name returns the name used to register the session.
+func (s *Session) Name() string {
+	return s.name
+}
+
+// Store returns the session store used to register the session.
+func (s *Session) Store() Store {
+	return s.store
+}
+
+// Registry -------------------------------------------------------------------
+
+// sessionInfo stores a session tracked by the registry.
+type sessionInfo struct {
+	s *Session
+	e error
+}
+
+// contextKey is the type used to store the registry in the context.
+type contextKey int
+
+// registryKey is the key used to store the registry in the context.
+const registryKey contextKey = 0
+
+// GetRegistry returns a registry instance for the current request.
+func GetRegistry(r *http.Request) *Registry {
+	var ctx = r.Context()
+	registry := ctx.Value(registryKey)
+	if registry != nil {
+		return registry.(*Registry)
+	}
+	newRegistry := &Registry{
+		request:  r,
+		sessions: make(map[string]sessionInfo),
+	}
+	*r = *r.WithContext(context.WithValue(ctx, registryKey, newRegistry))
+	return newRegistry
+}
+
+// Registry stores sessions used during a request.
+type Registry struct {
+	request  *http.Request
+	sessions map[string]sessionInfo
+}
+
+// Get registers and returns a session for the given name and session store.
+//
+// It returns a new session if there are no sessions registered for the name.
+func (s *Registry) Get(store Store, name string) (session *Session, err error) {
+	if !isCookieNameValid(name) {
+		return nil, fmt.Errorf("sessions: invalid character in cookie name: %s", name)
+	}
+	if info, ok := s.sessions[name]; ok {
+		session, err = info.s, info.e
+	} else {
+		session, err = store.New(s.request, name)
+		session.name = name
+		s.sessions[name] = sessionInfo{s: session, e: err}
+	}
+	session.store = store
+	return
+}
+
+// Save saves all sessions registered for the current request.
+func (s *Registry) Save(w http.ResponseWriter) error {
+	var errMulti MultiError
+	for name, info := range s.sessions {
+		session := info.s
+		if session.store == nil {
+			errMulti = append(errMulti, fmt.Errorf(
+				"sessions: missing store for session %q", name))
+		} else if err := session.store.Save(s.request, w, session); err != nil {
+			errMulti = append(errMulti, fmt.Errorf(
+				"sessions: error saving session %q -- %v", name, err))
+		}
+	}
+	if errMulti != nil {
+		return errMulti
+	}
+	return nil
+}
+
+// Helpers --------------------------------------------------------------------
+
+func init() {
+	gob.Register([]interface{}{})
+}
+
+// Save saves all sessions used during the current request.
+func Save(r *http.Request, w http.ResponseWriter) error {
+	return GetRegistry(r).Save(w)
+}
+
+// NewCookie returns an http.Cookie with the options set. It also sets
+// the Expires field calculated based on the MaxAge value, for Internet
+// Explorer compatibility.
+func NewCookie(name, value string, options *Options) *http.Cookie {
+	cookie := newCookieFromOptions(name, value, options)
+	if options.MaxAge > 0 {
+		d := time.Duration(options.MaxAge) * time.Second
+		cookie.Expires = time.Now().Add(d)
+	} else if options.MaxAge < 0 {
+		// Set it to the past to expire now.
+		cookie.Expires = time.Unix(1, 0)
+	}
+	return cookie
+}
+
+// Error ----------------------------------------------------------------------
+
+// MultiError stores multiple errors.
+//
+// Borrowed from the App Engine SDK.
+type MultiError []error
+
+func (m MultiError) Error() string {
+	s, n := "", 0
+	for _, e := range m {
+		if e != nil {
+			if n == 0 {
+				s = e.Error()
+			}
+			n++
+		}
+	}
+	switch n {
+	case 0:
+		return "(0 errors)"
+	case 1:
+		return s
+	case 2:
+		return s + " (and 1 other error)"
+	}
+	return fmt.Sprintf("%s (and %d other errors)", s, n-1)
+}
--- a/vendor/github.com/gorilla/sessions/store.go
+++ b/vendor/github.com/gorilla/sessions/store.go
@ -0,0 +1,292 @@
+// Copyright 2012 The Gorilla Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sessions
+
+import (
+	"encoding/base32"
+	"io/ioutil"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+
+	"github.com/gorilla/securecookie"
+)
+
+// Store is an interface for custom session stores.
+//
+// See CookieStore and FilesystemStore for examples.
+type Store interface {
+	// Get should return a cached session.
+	Get(r *http.Request, name string) (*Session, error)
+
+	// New should create and return a new session.
+	//
+	// Note that New should never return a nil session, even in the case of
+	// an error if using the Registry infrastructure to cache the session.
+	New(r *http.Request, name string) (*Session, error)
+
+	// Save should persist session to the underlying store implementation.
+	Save(r *http.Request, w http.ResponseWriter, s *Session) error
+}
+
+// CookieStore ----------------------------------------------------------------
+
+// NewCookieStore returns a new CookieStore.
+//
+// Keys are defined in pairs to allow key rotation, but the common case is
+// to set a single authentication key and optionally an encryption key.
+//
+// The first key in a pair is used for authentication and the second for
+// encryption. The encryption key can be set to nil or omitted in the last
+// pair, but the authentication key is required in all pairs.
+//
+// It is recommended to use an authentication key with 32 or 64 bytes.
+// The encryption key, if set, must be either 16, 24, or 32 bytes to select
+// AES-128, AES-192, or AES-256 modes.
+func NewCookieStore(keyPairs ...[]byte) *CookieStore {
+	cs := &CookieStore{
+		Codecs: securecookie.CodecsFromPairs(keyPairs...),
+		Options: &Options{
+			Path:   "/",
+			MaxAge: 86400 * 30,
+		},
+	}
+
+	cs.MaxAge(cs.Options.MaxAge)
+	return cs
+}
+
+// CookieStore stores sessions using secure cookies.
+type CookieStore struct {
+	Codecs  []securecookie.Codec
+	Options *Options // default configuration
+}
+
+// Get returns a session for the given name after adding it to the registry.
+//
+// It returns a new session if the sessions doesn't exist. Access IsNew on
+// the session to check if it is an existing session or a new one.
+//
+// It returns a new session and an error if the session exists but could
+// not be decoded.
+func (s *CookieStore) Get(r *http.Request, name string) (*Session, error) {
+	return GetRegistry(r).Get(s, name)
+}
+
+// New returns a session for the given name without adding it to the registry.
+//
+// The difference between New() and Get() is that calling New() twice will
+// decode the session data twice, while Get() registers and reuses the same
+// decoded session after the first call.
+func (s *CookieStore) New(r *http.Request, name string) (*Session, error) {
+	session := NewSession(s, name)
+	opts := *s.Options
+	session.Options = &opts
+	session.IsNew = true
+	var err error
+	if c, errCookie := r.Cookie(name); errCookie == nil {
+		err = securecookie.DecodeMulti(name, c.Value, &session.Values,
+			s.Codecs...)
+		if err == nil {
+			session.IsNew = false
+		}
+	}
+	return session, err
+}
+
+// Save adds a single session to the response.
+func (s *CookieStore) Save(r *http.Request, w http.ResponseWriter,
+	session *Session) error {
+	encoded, err := securecookie.EncodeMulti(session.Name(), session.Values,
+		s.Codecs...)
+	if err != nil {
+		return err
+	}
+	http.SetCookie(w, NewCookie(session.Name(), encoded, session.Options))
+	return nil
+}
+
+// MaxAge sets the maximum age for the store and the underlying cookie
+// implementation. Individual sessions can be deleted by setting Options.MaxAge
+// = -1 for that session.
+func (s *CookieStore) MaxAge(age int) {
+	s.Options.MaxAge = age
+
+	// Set the maxAge for each securecookie instance.
+	for _, codec := range s.Codecs {
+		if sc, ok := codec.(*securecookie.SecureCookie); ok {
+			sc.MaxAge(age)
+		}
+	}
+}
+
+// FilesystemStore ------------------------------------------------------------
+
+var fileMutex sync.RWMutex
+
+// NewFilesystemStore returns a new FilesystemStore.
+//
+// The path argument is the directory where sessions will be saved. If empty
+// it will use os.TempDir().
+//
+// See NewCookieStore() for a description of the other parameters.
+func NewFilesystemStore(path string, keyPairs ...[]byte) *FilesystemStore {
+	if path == "" {
+		path = os.TempDir()
+	}
+	fs := &FilesystemStore{
+		Codecs: securecookie.CodecsFromPairs(keyPairs...),
+		Options: &Options{
+			Path:   "/",
+			MaxAge: 86400 * 30,
+		},
+		path: path,
+	}
+
+	fs.MaxAge(fs.Options.MaxAge)
+	return fs
+}
+
+// FilesystemStore stores sessions in the filesystem.
+//
+// It also serves as a reference for custom stores.
+//
+// This store is still experimental and not well tested. Feedback is welcome.
+type FilesystemStore struct {
+	Codecs  []securecookie.Codec
+	Options *Options // default configuration
+	path    string
+}
+
+// MaxLength restricts the maximum length of new sessions to l.
+// If l is 0 there is no limit to the size of a session, use with caution.
+// The default for a new FilesystemStore is 4096.
+func (s *FilesystemStore) MaxLength(l int) {
+	for _, c := range s.Codecs {
+		if codec, ok := c.(*securecookie.SecureCookie); ok {
+			codec.MaxLength(l)
+		}
+	}
+}
+
+// Get returns a session for the given name after adding it to the registry.
+//
+// See CookieStore.Get().
+func (s *FilesystemStore) Get(r *http.Request, name string) (*Session, error) {
+	return GetRegistry(r).Get(s, name)
+}
+
+// New returns a session for the given name without adding it to the registry.
+//
+// See CookieStore.New().
+func (s *FilesystemStore) New(r *http.Request, name string) (*Session, error) {
+	session := NewSession(s, name)
+	opts := *s.Options
+	session.Options = &opts
+	session.IsNew = true
+	var err error
+	if c, errCookie := r.Cookie(name); errCookie == nil {
+		err = securecookie.DecodeMulti(name, c.Value, &session.ID, s.Codecs...)
+		if err == nil {
+			err = s.load(session)
+			if err == nil {
+				session.IsNew = false
+			}
+		}
+	}
+	return session, err
+}
+
+// Save adds a single session to the response.
+//
+// If the Options.MaxAge of the session is <= 0 then the session file will be
+// deleted from the store path. With this process it enforces the properly
+// session cookie handling so no need to trust in the cookie management in the
+// web browser.
+func (s *FilesystemStore) Save(r *http.Request, w http.ResponseWriter,
+	session *Session) error {
+	// Delete if max-age is <= 0
+	if session.Options.MaxAge <= 0 {
+		if err := s.erase(session); err != nil {
+			return err
+		}
+		http.SetCookie(w, NewCookie(session.Name(), "", session.Options))
+		return nil
+	}
+
+	if session.ID == "" {
+		// Because the ID is used in the filename, encode it to
+		// use alphanumeric characters only.
+		session.ID = strings.TrimRight(
+			base32.StdEncoding.EncodeToString(
+				securecookie.GenerateRandomKey(32)), "=")
+	}
+	if err := s.save(session); err != nil {
+		return err
+	}
+	encoded, err := securecookie.EncodeMulti(session.Name(), session.ID,
+		s.Codecs...)
+	if err != nil {
+		return err
+	}
+	http.SetCookie(w, NewCookie(session.Name(), encoded, session.Options))
+	return nil
+}
+
+// MaxAge sets the maximum age for the store and the underlying cookie
+// implementation. Individual sessions can be deleted by setting Options.MaxAge
+// = -1 for that session.
+func (s *FilesystemStore) MaxAge(age int) {
+	s.Options.MaxAge = age
+
+	// Set the maxAge for each securecookie instance.
+	for _, codec := range s.Codecs {
+		if sc, ok := codec.(*securecookie.SecureCookie); ok {
+			sc.MaxAge(age)
+		}
+	}
+}
+
+// save writes encoded session.Values to a file.
+func (s *FilesystemStore) save(session *Session) error {
+	encoded, err := securecookie.EncodeMulti(session.Name(), session.Values,
+		s.Codecs...)
+	if err != nil {
+		return err
+	}
+	filename := filepath.Join(s.path, "session_"+session.ID)
+	fileMutex.Lock()
+	defer fileMutex.Unlock()
+	return ioutil.WriteFile(filename, []byte(encoded), 0600)
+}
+
+// load reads a file and decodes its content into session.Values.
+func (s *FilesystemStore) load(session *Session) error {
+	filename := filepath.Join(s.path, "session_"+session.ID)
+	fileMutex.RLock()
+	defer fileMutex.RUnlock()
+	fdata, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return err
+	}
+	if err = securecookie.DecodeMulti(session.Name(), string(fdata),
+		&session.Values, s.Codecs...); err != nil {
+		return err
+	}
+	return nil
+}
+
+// delete session file
+func (s *FilesystemStore) erase(session *Session) error {
+	filename := filepath.Join(s.path, "session_"+session.ID)
+
+	fileMutex.RLock()
+	defer fileMutex.RUnlock()
+
+	err := os.Remove(filename)
+	return err
+}
--- a/vendor/modules.txt
+++ b/vendor/modules.txt
@ -351,6 +351,12 @@ github.com/google/gopacket/routing
 # github.com/google/uuid v1.3.0
 ## explicit
 github.com/google/uuid
+# github.com/gorilla/securecookie v1.1.1
+## explicit
+github.com/gorilla/securecookie
+# github.com/gorilla/sessions v1.2.1
+## explicit
+github.com/gorilla/sessions
 # github.com/gorilla/websocket v1.5.0
 ## explicit; go 1.12
 github.com/gorilla/websocket