grpc client in tls mode (#19680)

* client in tls mode

command/resource/client/client.go

@@ -6,7 +6,6 @@ package client
 import (
 	"bytes"
 	"context"
-	"crypto/tls"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -21,7 +20,6 @@ import (
 
 	"github.com/hashicorp/go-cleanhttp"
 	"github.com/hashicorp/go-hclog"
-	"github.com/hashicorp/go-rootcerts"
 
 	"github.com/hashicorp/consul/api"
 )
@@ -73,14 +71,6 @@ const (
 	// whether or not to disable certificate checking.
 	HTTPSSLVerifyEnvName = "CONSUL_HTTP_SSL_VERIFY"
 
-	// GRPCCAFileEnvName defines an environment variable name which sets the
-	// CA file to use for talking to Consul gRPC over TLS.
-	GRPCCAFileEnvName = "CONSUL_GRPC_CACERT"
-
-	// GRPCCAPathEnvName defines an environment variable name which sets the
-	// path to a directory of CA certs to use for talking to Consul gRPC over TLS.
-	GRPCCAPathEnvName = "CONSUL_GRPC_CAPATH"
-
 	// HTTPNamespaceEnvVar defines an environment variable name which sets
 	// the HTTP Namespace to be used by default. This can still be overridden.
 	HTTPNamespaceEnvName = "CONSUL_NAMESPACE"
@@ -538,60 +528,6 @@ func defaultConfig(logger hclog.Logger, transportFn func() *http.Transport) *Con
 	return config
 }
 
-// TLSConfig is used to generate a TLSClientConfig that's useful for talking to
-// Consul using TLS.
-func SetupTLSConfig(tlsConfig *TLSConfig) (*tls.Config, error) {
-	tlsClientConfig := &tls.Config{
-		InsecureSkipVerify: tlsConfig.InsecureSkipVerify,
-	}
-
-	if tlsConfig.Address != "" {
-		server := tlsConfig.Address
-		hasPort := strings.LastIndex(server, ":") > strings.LastIndex(server, "]")
-		if hasPort {
-			var err error
-			server, _, err = net.SplitHostPort(server)
-			if err != nil {
-				return nil, err
-			}
-		}
-		tlsClientConfig.ServerName = server
-	}
-
-	if len(tlsConfig.CertPEM) != 0 && len(tlsConfig.KeyPEM) != 0 {
-		tlsCert, err := tls.X509KeyPair(tlsConfig.CertPEM, tlsConfig.KeyPEM)
-		if err != nil {
-			return nil, err
-		}
-		tlsClientConfig.Certificates = []tls.Certificate{tlsCert}
-	} else if len(tlsConfig.CertPEM) != 0 || len(tlsConfig.KeyPEM) != 0 {
-		return nil, fmt.Errorf("both client cert and client key must be provided")
-	}
-
-	if tlsConfig.CertFile != "" && tlsConfig.KeyFile != "" {
-		tlsCert, err := tls.LoadX509KeyPair(tlsConfig.CertFile, tlsConfig.KeyFile)
-		if err != nil {
-			return nil, err
-		}
-		tlsClientConfig.Certificates = []tls.Certificate{tlsCert}
-	} else if tlsConfig.CertFile != "" || tlsConfig.KeyFile != "" {
-		return nil, fmt.Errorf("both client cert and client key must be provided")
-	}
-
-	if tlsConfig.CAFile != "" || tlsConfig.CAPath != "" || len(tlsConfig.CAPem) != 0 {
-		rootConfig := &rootcerts.Config{
-			CAFile:        tlsConfig.CAFile,
-			CAPath:        tlsConfig.CAPath,
-			CACertificate: tlsConfig.CAPem,
-		}
-		if err := rootcerts.ConfigureTLS(tlsClientConfig, rootConfig); err != nil {
-			return nil, err
-		}
-	}
-
-	return tlsClientConfig, nil
-}
-
 func (c *Config) GenerateEnv() []string {
 	env := make([]string, 0, 10)
 

command/resource/client/grpc-client.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/credentials/insecure"
 
 	"github.com/hashicorp/consul/proto-public/pbresource"
@@ -31,9 +32,34 @@ func NewGRPCClient(config *GRPCConfig) (*GRPCClient, error) {
 }
 
 func dial(c *GRPCConfig) (*grpc.ClientConn, error) {
-	// TODO: decide if we use TLS mode based on the config
-	dialOpts := []grpc.DialOption{
-		grpc.WithTransportCredentials(insecure.NewCredentials()),
+	err := checkCertificates(c)
+	if err != nil {
+		return nil, err
 	}
+	var dialOpts []grpc.DialOption
+	if c.GRPCTLS {
+		tlsConfig, err := SetupTLSConfig(c)
+		if err != nil {
+			return nil, fmt.Errorf("failed to setup tls config when tried to establish grpc call: %w", err)
+		}
+		dialOpts = append(dialOpts, grpc.WithTransportCredentials(credentials.NewTLS(tlsConfig)))
+	} else {
+		dialOpts = append(dialOpts, grpc.WithTransportCredentials(insecure.NewCredentials()))
+	}
+
 	return grpc.Dial(c.Address, dialOpts...)
 }
+
+func checkCertificates(c *GRPCConfig) error {
+	if c.GRPCTLS {
+		certFileEmpty := c.CertFile == ""
+		keyFileEmpty := c.CertFile == ""
+
+		// both files need to be empty or both files need to be provided
+		if certFileEmpty != keyFileEmpty {
+			return fmt.Errorf("you have to provide client certificate file and key file at the same time " +
+				"if you intend to communicate in TLS/SSL mode")
+		}
+	}
+	return nil
+}

command/resource/client/grpc-client_test.go

@@ -9,23 +9,27 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 	"google.golang.org/protobuf/proto"
 
 	"github.com/hashicorp/consul/agent"
 	"github.com/hashicorp/consul/internal/resource/demo"
 	"github.com/hashicorp/consul/proto-public/pbresource"
 	"github.com/hashicorp/consul/proto/private/prototest"
+	"github.com/hashicorp/consul/sdk/freeport"
 	"github.com/hashicorp/consul/sdk/testutil"
 	"github.com/hashicorp/consul/testrpc"
 )
 
 func TestResourceRead(t *testing.T) {
-	t.Parallel()
-
-	a := agent.NewTestAgent(t, "ports { grpc = 8502 }")
+	availablePort := freeport.GetOne(t)
+	a := agent.NewTestAgent(t, fmt.Sprintf("ports { grpc = %d }", availablePort))
 	testrpc.WaitForTestAgent(t, a.RPC, "dc1")
-	grpcConfig := GetDefaultGRPCConfig()
+	grpcConfig, err := LoadGRPCConfig(&GRPCConfig{Address: fmt.Sprintf("127.0.0.1:%d", availablePort)})
+	require.NoError(t, err)
 	gRPCClient, err := NewGRPCClient(grpcConfig)
+	require.NoError(t, err)
 
 	t.Cleanup(func() {
 		a.Shutdown()
@@ -49,3 +53,95 @@ func TestResourceRead(t *testing.T) {
 		prototest.AssertDeepEqual(t, writeRsp.Resource, readRsp.Resource)
 	})
 }
+
+func TestResourceReadInTLS(t *testing.T) {
+	tests := []struct {
+		name              string
+		requireClientCert bool
+		grpcConfig        func() (*GRPCConfig, int)
+	}{
+		{
+			name:              "Test with CertFile, KeyFile and CAFile",
+			requireClientCert: true,
+			grpcConfig: func() (*GRPCConfig, int) {
+				availablePort := freeport.GetOne(t)
+				return &GRPCConfig{
+					Address:  fmt.Sprintf("127.0.0.1:%d", availablePort),
+					GRPCTLS:  true,
+					CertFile: "../../../test/client_certs/client.crt",
+					KeyFile:  "../../../test/client_certs/client.key",
+					CAFile:   "../../../test/client_certs/rootca.crt",
+				}, availablePort
+			},
+		},
+		{
+			name:              "Test without CAFile",
+			requireClientCert: true,
+			grpcConfig: func() (*GRPCConfig, int) {
+				availablePort := freeport.GetOne(t)
+				return &GRPCConfig{
+					Address:       fmt.Sprintf("127.0.0.1:%d", availablePort),
+					GRPCTLS:       true,
+					GRPCTLSVerify: false,
+					CertFile:      "../../../test/client_certs/client.crt",
+					KeyFile:       "../../../test/client_certs/client.key",
+				}, availablePort
+			},
+		},
+		{
+			name:              "Test without client certificates",
+			requireClientCert: false,
+			grpcConfig: func() (*GRPCConfig, int) {
+				availablePort := freeport.GetOne(t)
+				return &GRPCConfig{
+					Address: fmt.Sprintf("127.0.0.1:%d", availablePort),
+					GRPCTLS: true,
+				}, availablePort
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			grpcClientConfig, availablePort := tt.grpcConfig()
+			a := agent.StartTestAgent(t, agent.TestAgent{
+				HCL: fmt.Sprintf(`
+					ports { grpc_tls = %d }
+					enable_agent_tls_for_checks = true
+					tls {
+						defaults {
+							verify_incoming = %t
+							key_file = "../../../test/client_certs/server.key"
+							cert_file = "../../../test/client_certs/server.crt"
+							ca_file = "../../../test/client_certs/rootca.crt"
+						}
+					}`, availablePort, tt.requireClientCert),
+				UseGRPCTLS: true,
+			})
+			testrpc.WaitForTestAgent(t, a.RPC, "dc1")
+			grpcConfig, err := LoadGRPCConfig(grpcClientConfig)
+			require.NoError(t, err)
+			gRPCClient, err := NewGRPCClient(grpcConfig)
+			require.NoError(t, err)
+
+			t.Cleanup(func() {
+				a.Shutdown()
+				gRPCClient.Conn.Close()
+			})
+
+			v2Artist, err := demo.GenerateV2Artist()
+			require.NoError(t, err)
+
+			_, err = gRPCClient.Client.Read(context.Background(), &pbresource.ReadRequest{Id: v2Artist.Id})
+			require.Equal(t, codes.NotFound.String(), status.Code(err).String())
+
+			writeRsp, err := gRPCClient.Client.Write(testutil.TestContext(t), &pbresource.WriteRequest{Resource: v2Artist})
+			require.NoError(t, err)
+
+			readRsp, err := gRPCClient.Client.Read(context.Background(), &pbresource.ReadRequest{Id: v2Artist.Id})
+			require.NoError(t, err)
+			require.Equal(t, proto.Equal(readRsp.Resource.Id.Type, demo.TypeV2Artist), true)
+			prototest.AssertDeepEqual(t, writeRsp.Resource, readRsp.Resource)
+		})
+	}
+}

command/resource/client/grpc-config.go

@@ -4,40 +4,132 @@
 package client
 
 import (
+	"fmt"
 	"os"
+	"strconv"
+	"strings"
 )
 
 const (
 	// GRPCAddrEnvName defines an environment variable name which sets the gRPC
 	// server address for the consul CLI.
 	GRPCAddrEnvName = "CONSUL_GRPC_ADDR"
+
+	// GRPCTLSEnvName defines an environment variable name which sets the gRPC
+	// communication mode. Default is false in plaintext mode.
+	GRPCTLSEnvName = "CONSUL_GRPC_TLS"
+
+	// GRPCTLSVerifyEnvName defines an environment variable name which sets
+	// whether to disable certificate checking.
+	GRPCTLSVerifyEnvName = "CONSUL_GRPC_TLS_VERIFY"
+
+	// GRPCClientCertEnvName defines an environment variable name which sets the
+	// client cert file to use for talking to Consul over TLS.
+	GRPCClientCertEnvName = "CONSUL_GRPC_CLIENT_CERT"
+
+	// GRPCClientKeyEnvName defines an environment variable name which sets the
+	// client key file to use for talking to Consul over TLS.
+	GRPCClientKeyEnvName = "CONSUL_GRPC_CLIENT_KEY"
+
+	// GRPCCAFileEnvName defines an environment variable name which sets the
+	// CA file to use for talking to Consul gRPC over TLS.
+	GRPCCAFileEnvName = "CONSUL_GRPC_CACERT"
+
+	// GRPCCAPathEnvName defines an environment variable name which sets the
+	// path to a directory of CA certs to use for talking to Consul gRPC over TLS.
+	GRPCCAPathEnvName = "CONSUL_GRPC_CAPATH"
 )
 
 type GRPCConfig struct {
+	// Address is the optional address of the Consul server in format of host:port.
+	// It doesn't include schema
 	Address string
+
+	// GRPCTLS is the optional boolean flag to determine the communication protocol
+	GRPCTLS bool
+
+	// GRPCTLSVerify is the optional boolean flag to disable certificate checking.
+	// Set to false only if you want to skip server verification
+	GRPCTLSVerify bool
+
+	// CertFile is the optional path to the certificate for Consul
+	// communication. If this is set then you need to also set KeyFile.
+	CertFile string
+
+	// KeyFile is the optional path to the private key for Consul communication.
+	// If this is set then you need to also set CertFile.
+	KeyFile string
+
+	// CAFile is the optional path to the CA certificate used for Consul
+	// communication, defaults to the system bundle if not specified.
+	CAFile string
+
+	// CAPath is the optional path to a directory of CA certificates to use for
+	// Consul communication, defaults to the system bundle if not specified.
+	CAPath string
 }
 
 func GetDefaultGRPCConfig() *GRPCConfig {
 	return &GRPCConfig{
-		Address: "localhost:8502",
+		Address:       "127.0.0.1:8502",
+		GRPCTLSVerify: false,
 	}
 }
 
-func LoadGRPCConfig(defaultConfig *GRPCConfig) *GRPCConfig {
+func LoadGRPCConfig(defaultConfig *GRPCConfig) (*GRPCConfig, error) {
 	if defaultConfig == nil {
 		defaultConfig = GetDefaultGRPCConfig()
 	}
 
-	overwrittenConfig := loadEnvToDefaultConfig(defaultConfig)
-
-	return overwrittenConfig
-}
-
-func loadEnvToDefaultConfig(config *GRPCConfig) *GRPCConfig {
-
-	if addr := os.Getenv(GRPCAddrEnvName); addr != "" {
-		config.Address = addr
+	overwrittenConfig, err := loadEnvToDefaultConfig(defaultConfig)
+	if err != nil {
+		return nil, err
 	}
 
-	return config
+	return overwrittenConfig, nil
+}
+
+func loadEnvToDefaultConfig(config *GRPCConfig) (*GRPCConfig, error) {
+	if addr := os.Getenv(GRPCAddrEnvName); addr != "" {
+		if strings.HasPrefix(strings.ToLower(addr), "https://") {
+			config.GRPCTLS = true
+		}
+		config.Address = removeSchemaFromGRPCAddress(addr)
+	}
+
+	if tlsMode := os.Getenv(GRPCTLSEnvName); tlsMode != "" {
+		doTLS, err := strconv.ParseBool(tlsMode)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse %s: %w", GRPCTLSEnvName, err)
+		}
+		if doTLS {
+			config.GRPCTLS = true
+		}
+	}
+
+	if v := os.Getenv(GRPCTLSVerifyEnvName); v != "" {
+		doVerify, err := strconv.ParseBool(v)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse %s: %w", GRPCTLSVerifyEnvName, err)
+		}
+		config.GRPCTLSVerify = doVerify
+	}
+
+	if v := os.Getenv(GRPCClientCertEnvName); v != "" {
+		config.CertFile = v
+	}
+
+	if v := os.Getenv(GRPCClientKeyEnvName); v != "" {
+		config.KeyFile = v
+	}
+
+	if caFile := os.Getenv(GRPCCAFileEnvName); caFile != "" {
+		config.CAFile = caFile
+	}
+
+	if caPath := os.Getenv(GRPCCAPathEnvName); caPath != "" {
+		config.CAPath = caPath
+	}
+
+	return config, nil
 }

command/resource/client/grpc-config_test.go

@@ -0,0 +1,56 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: BUSL-1.1
+
+package client
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLoadGRPCConfig(t *testing.T) {
+	t.Run("Default Config", func(t *testing.T) {
+		// Test when defaultConfig is nil
+		config, err := LoadGRPCConfig(nil)
+		assert.NoError(t, err)
+		assert.Equal(t, GetDefaultGRPCConfig(), config)
+	})
+
+	// Test when environment variables are set
+	t.Run("Env Overwritten", func(t *testing.T) {
+		// Mock environment variables
+		t.Setenv(GRPCAddrEnvName, "localhost:8500")
+		t.Setenv(GRPCTLSEnvName, "true")
+		t.Setenv(GRPCTLSVerifyEnvName, "false")
+		t.Setenv(GRPCClientCertEnvName, "/path/to/client.crt")
+		t.Setenv(GRPCClientKeyEnvName, "/path/to/client.key")
+		t.Setenv(GRPCCAFileEnvName, "/path/to/ca.crt")
+		t.Setenv(GRPCCAPathEnvName, "/path/to/cacerts")
+
+		// Load and validate the configuration
+		config, err := LoadGRPCConfig(nil)
+		assert.NoError(t, err)
+		expectedConfig := &GRPCConfig{
+			Address:       "localhost:8500",
+			GRPCTLS:       true,
+			GRPCTLSVerify: false,
+			CertFile:      "/path/to/client.crt",
+			KeyFile:       "/path/to/client.key",
+			CAFile:        "/path/to/ca.crt",
+			CAPath:        "/path/to/cacerts",
+		}
+		assert.Equal(t, expectedConfig, config)
+	})
+
+	// Test when there's an error parsing a boolean value from an environment variable
+	t.Run("Error Parsing Bool", func(t *testing.T) {
+		// Mock environment variable with an invalid boolean value
+		t.Setenv(GRPCTLSEnvName, "invalid_boolean_value")
+
+		// Load and expect an error
+		config, err := LoadGRPCConfig(nil)
+		assert.Error(t, err, "failed to parse CONSUL_GRPC_TLS: strconv.ParseBool: parsing \"invalid_boolean_value\": invalid syntax")
+		assert.Nil(t, config)
+	})
+}

command/resource/client/grpc-flags.go

@@ -5,54 +5,60 @@ package client
 
 import (
 	"flag"
+	"strings"
 )
 
 type GRPCFlags struct {
-	address StringValue
+	address  TValue[string]
+	grpcTLS  TValue[bool]
+	certFile TValue[string]
+	keyFile  TValue[string]
+	caFile   TValue[string]
+	caPath   TValue[string]
 }
 
-// mergeFlagsIntoGRPCConfig merges flag values into grpc config
+// MergeFlagsIntoGRPCConfig merges flag values into grpc config
 // caller has to parse the CLI args before loading them into flag values
-func (f *GRPCFlags) mergeFlagsIntoGRPCConfig(c *GRPCConfig) {
+// The flags take precedence over the environment values
+func (f *GRPCFlags) MergeFlagsIntoGRPCConfig(c *GRPCConfig) {
+	if strings.HasPrefix(strings.ToLower(f.address.String()), "https://") {
+		c.GRPCTLS = true
+	}
+	f.address.Set(removeSchemaFromGRPCAddress(f.address.String()))
 	f.address.Merge(&c.Address)
+	// won't overwrite the value if it's false
+	if f.grpcTLS.v != nil && *f.grpcTLS.v {
+		f.grpcTLS.Merge(&c.GRPCTLS)
+	}
+	f.certFile.Merge(&c.CertFile)
+	f.keyFile.Merge(&c.KeyFile)
+	f.caFile.Merge(&c.CAFile)
+	f.caPath.Merge(&c.CAPath)
 }
 
+// merge the client flags into command line flags then parse command line flags
 func (f *GRPCFlags) ClientFlags() *flag.FlagSet {
 	fs := flag.NewFlagSet("", flag.ContinueOnError)
 	fs.Var(&f.address, "grpc-addr",
-		"The `address` and port of the Consul GRPC agent. The value can be an IP "+
-			"address or DNS address, but it must also include the port. This can "+
-			"also be specified via the CONSUL_GRPC_ADDR environment variable. The "+
-			"default value is 127.0.0.1:8502. It supports TLS communication "+
-			"by setting the environment variable CONSUL_GRPC_TLS=true.")
+		"The `address` and `port` of the Consul GRPC agent. The value can be an IP "+
+			"address or DNS address, but it must also include the port. This can also be specified "+
+			"via the CONSUL_GRPC_ADDR environment variable. The default value is "+
+			"127.0.0.1:8502. If you intend to communicate in TLS mode, you have to either "+
+			"include https:// schema in the address, use grpc-tls flag or set environment variable "+
+			"CONSUL_GRPC_TLS = true, otherwise it uses plaintext mode")
+	fs.Var(&f.caFile, "grpc-tls",
+		"Set to true if you aim to communicate in TLS mode in the GRPC call.")
+	fs.Var(&f.certFile, "client-cert",
+		"Path to a client cert file to use for TLS when 'verify_incoming' is enabled. This "+
+			"can also be specified via the CONSUL_GRPC_CLIENT_CERT environment variable.")
+	fs.Var(&f.keyFile, "client-key",
+		"Path to a client key file to use for TLS when 'verify_incoming' is enabled. This "+
+			"can also be specified via the CONSUL_GRPC_CLIENT_KEY environment variable.")
+	fs.Var(&f.caFile, "ca-file",
+		"Path to a CA file to use for TLS when communicating with Consul. This "+
+			"can also be specified via the CONSUL_CACERT environment variable.")
+	fs.Var(&f.caPath, "ca-path",
+		"Path to a directory of CA certificates to use for TLS when communicating "+
+			"with Consul. This can also be specified via the CONSUL_CAPATH environment variable.")
 	return fs
 }
-
-type StringValue struct {
-	v *string
-}
-
-// Set implements the flag.Value interface.
-func (s *StringValue) Set(v string) error {
-	if s.v == nil {
-		s.v = new(string)
-	}
-	*(s.v) = v
-	return nil
-}
-
-// String implements the flag.Value interface.
-func (s *StringValue) String() string {
-	var current string
-	if s.v != nil {
-		current = *(s.v)
-	}
-	return current
-}
-
-// Merge will overlay this value if it has been set.
-func (s *StringValue) Merge(onto *string) {
-	if s.v != nil {
-		*onto = *(s.v)
-	}
-}

command/resource/client/grpc-flags_test.go

@@ -0,0 +1,98 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: BUSL-1.1
+
+package client
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMergeFlagsIntoGRPCConfig(t *testing.T) {
+	t.Run("MergeFlagsIntoGRPCConfig", func(t *testing.T) {
+		// Setup GRPCFlags with some flag values
+		flags := &GRPCFlags{
+			address:  TValue[string]{v: stringPointer("https://example.com:8502")},
+			grpcTLS:  TValue[bool]{v: boolPointer(true)},
+			certFile: TValue[string]{v: stringPointer("/path/to/client.crt")},
+			keyFile:  TValue[string]{v: stringPointer("/path/to/client.key")},
+			caFile:   TValue[string]{v: stringPointer("/path/to/ca.crt")},
+			caPath:   TValue[string]{v: stringPointer("/path/to/cacerts")},
+		}
+
+		// Setup GRPCConfig with some initial values
+		config := &GRPCConfig{
+			Address:       "localhost:8500",
+			GRPCTLS:       false,
+			GRPCTLSVerify: true,
+			CertFile:      "/path/to/default/client.crt",
+			KeyFile:       "/path/to/default/client.key",
+			CAFile:        "/path/to/default/ca.crt",
+			CAPath:        "/path/to/default/cacerts",
+		}
+
+		// Call MergeFlagsIntoGRPCConfig to merge flag values into the config
+		flags.MergeFlagsIntoGRPCConfig(config)
+
+		// Validate the merged config
+		expectedConfig := &GRPCConfig{
+			Address:       "example.com:8502",
+			GRPCTLS:       true,
+			GRPCTLSVerify: true,
+			CertFile:      "/path/to/client.crt",
+			KeyFile:       "/path/to/client.key",
+			CAFile:        "/path/to/ca.crt",
+			CAPath:        "/path/to/cacerts",
+		}
+
+		assert.Equal(t, expectedConfig, config)
+	})
+	t.Run("MergeFlagsIntoGRPCConfig: allow empty values", func(t *testing.T) {
+		// Setup GRPCFlags with some flag values
+		flags := &GRPCFlags{
+			address:  TValue[string]{v: stringPointer("http://example.com:8502")},
+			grpcTLS:  TValue[bool]{},
+			certFile: TValue[string]{v: stringPointer("/path/to/client.crt")},
+			keyFile:  TValue[string]{v: stringPointer("/path/to/client.key")},
+			caFile:   TValue[string]{v: stringPointer("/path/to/ca.crt")},
+			caPath:   TValue[string]{v: stringPointer("/path/to/cacerts")},
+		}
+
+		// Setup GRPCConfig with some initial values
+		config := &GRPCConfig{
+			Address:       "localhost:8500",
+			GRPCTLSVerify: true,
+			CertFile:      "/path/to/default/client.crt",
+			KeyFile:       "/path/to/default/client.key",
+			CAFile:        "/path/to/default/ca.crt",
+			CAPath:        "/path/to/default/cacerts",
+		}
+
+		// Call MergeFlagsIntoGRPCConfig to merge flag values into the config
+		flags.MergeFlagsIntoGRPCConfig(config)
+
+		// Validate the merged config
+		expectedConfig := &GRPCConfig{
+			Address:       "example.com:8502",
+			GRPCTLS:       false,
+			GRPCTLSVerify: true,
+			CertFile:      "/path/to/client.crt",
+			KeyFile:       "/path/to/client.key",
+			CAFile:        "/path/to/ca.crt",
+			CAPath:        "/path/to/cacerts",
+		}
+
+		assert.Equal(t, expectedConfig, config)
+	})
+}
+
+// Utility function to convert string to string pointer
+func stringPointer(s string) *string {
+	return &s
+}
+
+// Utility function to convert bool to bool pointer
+func boolPointer(b bool) *bool {
+	return &b
+}

command/resource/client/helper.go

@@ -0,0 +1,93 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: BUSL-1.1
+
+package client
+
+import (
+	"crypto/tls"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/hashicorp/go-rootcerts"
+)
+
+// tls.Config is used to establish communication in TLS mode
+func SetupTLSConfig(c *GRPCConfig) (*tls.Config, error) {
+	tlsConfig := &tls.Config{
+		InsecureSkipVerify: !c.GRPCTLSVerify,
+	}
+
+	if c.CertFile != "" && c.KeyFile != "" {
+		tlsCert, err := tls.LoadX509KeyPair(c.CertFile, c.KeyFile)
+		if err != nil {
+			return nil, err
+		}
+		tlsConfig.Certificates = []tls.Certificate{tlsCert}
+	}
+
+	var caConfig *rootcerts.Config
+	if c.CAFile != "" || c.CAPath != "" {
+		caConfig = &rootcerts.Config{
+			CAFile: c.CAFile,
+			CAPath: c.CAPath,
+		}
+	}
+	// load system CA certs if user doesn't provide any
+	if err := rootcerts.ConfigureTLS(tlsConfig, caConfig); err != nil {
+		return nil, err
+	}
+
+	return tlsConfig, nil
+}
+
+func removeSchemaFromGRPCAddress(addr string) string {
+	// Parse as host:port with option http prefix
+	grpcAddr := strings.TrimPrefix(addr, "http://")
+	grpcAddr = strings.TrimPrefix(grpcAddr, "https://")
+	return grpcAddr
+}
+
+type TValue[T string | bool] struct {
+	v *T
+}
+
+// Set implements the flag.Value interface.
+func (t *TValue[T]) Set(v string) error {
+	if t.v == nil {
+		t.v = new(T)
+	}
+	var err error
+	// have to use interface{}(t.v) to do type assertion
+	switch interface{}(t.v).(type) {
+	case *string:
+		// have to use interface{}(t.v).(*string) to assert t.v as *string
+		*(interface{}(t.v).(*string)) = v
+	case *bool:
+		// have to use interface{}(t.v).(*bool) to assert t.v as *bool
+		*(interface{}(t.v).(*bool)), err = strconv.ParseBool(v)
+	default:
+		err = fmt.Errorf("unsupported type %T", t.v)
+	}
+	return err
+}
+
+// String implements the flag.Value interface.
+func (t *TValue[T]) String() string {
+	var current T
+	if t.v != nil {
+		current = *(t.v)
+	}
+	return fmt.Sprintf("%v", current)
+}
+
+// Merge will overlay this value if it has been set.
+func (t *TValue[T]) Merge(onto *T) error {
+	if onto == nil {
+		return fmt.Errorf("onto is nil")
+	}
+	if t.v != nil {
+		*onto = *(t.v)
+	}
+	return nil
+}

command/resource/client/helper_test.go

@@ -0,0 +1,70 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: BUSL-1.1
+
+package client
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTValue(t *testing.T) {
+	t.Run("String: set", func(t *testing.T) {
+		var tv TValue[string]
+
+		err := tv.Set("testString")
+		assert.NoError(t, err)
+
+		assert.Equal(t, *tv.v, "testString")
+	})
+
+	t.Run("String: merge", func(t *testing.T) {
+		var tv TValue[string]
+		var onto string
+
+		testStr := "testString"
+		tv.v = &testStr
+		tv.Merge(&onto)
+
+		assert.Equal(t, onto, "testString")
+	})
+
+	t.Run("String: merge nil", func(t *testing.T) {
+		var tv TValue[string]
+		var onto *string = nil
+
+		testStr := "testString"
+		tv.v = &testStr
+		err := tv.Merge(onto)
+
+		assert.Equal(t, err.Error(), "onto is nil")
+	})
+
+	t.Run("Get string", func(t *testing.T) {
+		var tv TValue[string]
+		testStr := "testString"
+		tv.v = &testStr
+		assert.Equal(t, tv.String(), "testString")
+	})
+
+	t.Run("Bool: set", func(t *testing.T) {
+		var tv TValue[bool]
+
+		err := tv.Set("true")
+		assert.NoError(t, err)
+
+		assert.Equal(t, *tv.v, true)
+	})
+
+	t.Run("Bool: merge", func(t *testing.T) {
+		var tv TValue[bool]
+		var onto bool
+
+		testBool := true
+		tv.v = &testBool
+		tv.Merge(&onto)
+
+		assert.Equal(t, onto, true)
+	})
+}