proxycfg: Add a test to show the bug

When a token is not provided at registration, the agent token is not being used.

agent/proxycfg/manager_test.go

@@ -557,3 +557,48 @@ func testGenCacheKey(req cache.Request) string {
 	info := req.CacheInfo()
 	return path.Join(info.Key, info.Datacenter)
 }
+
+func TestManager_SyncState_DefaultToken(t *testing.T) {
+	types := NewTestCacheTypes(t)
+	c := TestCacheWithTypes(t, types)
+	logger := testutil.Logger(t)
+	tokens := new(token.Store)
+	tokens.UpdateUserToken("default-token", token.TokenSourceConfig)
+
+	state := local.NewState(local.Config{}, logger, tokens)
+	state.TriggerSyncChanges = func() {}
+
+	m, err := NewManager(ManagerConfig{
+		Cache:  c,
+		Health: &health.Client{Cache: c, CacheName: cachetype.HealthServicesName},
+		State:  state,
+		// TODO: Tokens: tokens,
+		Source: &structs.QuerySource{Datacenter: "dc1"},
+		Logger: logger,
+	})
+	require.NoError(t, err)
+	defer m.Close()
+
+	srv := &structs.NodeService{
+		Kind:    structs.ServiceKindConnectProxy,
+		ID:      "web-sidecar-proxy",
+		Service: "web-sidecar-proxy",
+		Port:    9999,
+		Meta:    map[string]string{},
+		Proxy: structs.ConnectProxyConfig{
+			DestinationServiceID:   "web",
+			DestinationServiceName: "web",
+			LocalServiceAddress:    "127.0.0.1",
+			LocalServicePort:       8080,
+			Config: map[string]interface{}{
+				"foo": "bar",
+			},
+		},
+	}
+
+	err = state.AddServiceWithChecks(srv, nil, "")
+	require.NoError(t, err)
+	m.syncState()
+
+	require.Equal(t, "default-token", m.proxies[srv.CompoundServiceID()].serviceInstance.token)
+}