refactor(auth): refactor GetGRPCTransportCredsAndEndpoint return type to struct (googleapis#11599)

* Embed google.golang.org/grpc/credentials.TransportCredentials interface in new struct type with additional data.

refs: googleapis#11588

Author: quartzmo

auth/grpctransport/grpctransport.go

@@ -262,13 +262,13 @@ func dial(ctx context.Context, secure bool, opts *Options) (*grpc.ClientConn, er
 		tOpts.EnableDirectPath = io.EnableDirectPath
 		tOpts.EnableDirectPathXds = io.EnableDirectPathXds
 	}
-	transportCreds, endpoint, err := transport.GetGRPCTransportCredsAndEndpoint(tOpts)
+	transportCreds, err := transport.GetGRPCTransportCredsAndEndpoint(tOpts)
 	if err != nil {
 		return nil, err
 	}
 
 	if !secure {
-		transportCreds = grpcinsecure.NewCredentials()
+		transportCreds.TransportCredentials = grpcinsecure.NewCredentials()
 	}
 
 	// Initialize gRPC dial options with transport-level security options.
@@ -324,9 +324,8 @@ func dial(ctx context.Context, secure bool, opts *Options) (*grpc.ClientConn, er
 				clientUniverseDomain: opts.UniverseDomain,
 			}),
 		)
-
 		// Attempt Direct Path
-		grpcOpts, endpoint = configureDirectPath(grpcOpts, opts, endpoint, creds)
+		grpcOpts, transportCreds.Endpoint = configureDirectPath(grpcOpts, opts, transportCreds.Endpoint, creds)
 	}
 
 	// Add tracing, but before the other options, so that clients can override the
@@ -335,7 +334,7 @@ func dial(ctx context.Context, secure bool, opts *Options) (*grpc.ClientConn, er
 	grpcOpts = addOpenTelemetryStatsHandler(grpcOpts, opts)
 	grpcOpts = append(grpcOpts, opts.GRPCDialOpts...)
 
-	return grpc.Dial(endpoint, grpcOpts...)
+	return grpc.Dial(transportCreds.Endpoint, grpcOpts...)
 }
 
 // grpcKeyProvider satisfies https://pkg.go.dev/google.golang.org/grpc/credentials#PerRPCCredentials.

auth/internal/transport/cba.go

@@ -120,13 +120,20 @@ func fixScheme(baseURL string) string {
 	return baseURL
 }
 
+// GRPCTransportCredentials embeds interface TransportCredentials with additional data.
+type GRPCTransportCredentials struct {
+	credentials.TransportCredentials
+	Endpoint string
+	// TransportType TransportType
+}
+
 // GetGRPCTransportCredsAndEndpoint returns an instance of
 // [google.golang.org/grpc/credentials.TransportCredentials], and the
 // corresponding endpoint to use for GRPC client.
-func GetGRPCTransportCredsAndEndpoint(opts *Options) (credentials.TransportCredentials, string, error) {
+func GetGRPCTransportCredsAndEndpoint(opts *Options) (*GRPCTransportCredentials, error) {
 	config, err := getTransportConfig(opts)
 	if err != nil {
-		return nil, "", err
+		return nil, err
 	}
 
 	defaultTransportCreds := credentials.NewTLS(&tls.Config{
@@ -144,13 +151,13 @@ func GetGRPCTransportCredsAndEndpoint(opts *Options) (credentials.TransportCrede
 			if config.s2aAddress != "" {
 				s2aAddr = config.s2aAddress
 			} else {
-				return defaultTransportCreds, config.endpoint, nil
+				return &GRPCTransportCredentials{defaultTransportCreds, config.endpoint}, nil
 			}
 		}
 	} else if config.s2aAddress != "" {
 		s2aAddr = config.s2aAddress
 	} else {
-		return defaultTransportCreds, config.endpoint, nil
+		return &GRPCTransportCredentials{defaultTransportCreds, config.endpoint}, nil
 	}
 
 	var fallbackOpts *s2a.FallbackOptions
@@ -168,9 +175,9 @@ func GetGRPCTransportCredsAndEndpoint(opts *Options) (credentials.TransportCrede
 	})
 	if err != nil {
 		// Use default if we cannot initialize S2A client transport credentials.
-		return defaultTransportCreds, config.endpoint, nil
+		return &GRPCTransportCredentials{defaultTransportCreds, config.endpoint}, nil
 	}
-	return s2aTransportCreds, config.s2aMTLSEndpoint, nil
+	return &GRPCTransportCredentials{s2aTransportCreds, config.s2aMTLSEndpoint}, nil
 }
 
 // GetHTTPTransportConfig returns a client certificate source and a function for

auth/internal/transport/cba_test.go

@@ -413,9 +413,9 @@ func TestGetGRPCTransportConfigAndEndpoint_S2A(t *testing.T) {
 			} else {
 				t.Setenv(googleAPIUseCertSource, "false")
 			}
-			_, endpoint, _ := GetGRPCTransportCredsAndEndpoint(tc.opts)
-			if tc.want != endpoint {
-				t.Fatalf("want endpoint: %s, got %s", tc.want, endpoint)
+			transportCreds, _ := GetGRPCTransportCredsAndEndpoint(tc.opts)
+			if tc.want != transportCreds.Endpoint {
+				t.Fatalf("want endpoint: %s, got %s", tc.want, transportCreds.Endpoint)
 			}
 		})
 	}
@@ -764,12 +764,12 @@ func TestGetGRPCTransportCredsAndEndpoint_UniverseDomain(t *testing.T) {
 			} else {
 				t.Setenv(googleAPIUseCertSource, "false")
 			}
-			_, endpoint, err := GetGRPCTransportCredsAndEndpoint(tc.opts)
+			transportCreds, err := GetGRPCTransportCredsAndEndpoint(tc.opts)
 			if err != nil {
 				t.Fatalf("err: %v", err)
 			} else {
-				if tc.wantEndpoint != endpoint {
-					t.Errorf("want endpoint: %s, got %s", tc.wantEndpoint, endpoint)
+				if tc.wantEndpoint != transportCreds.Endpoint {
+					t.Errorf("want endpoint: %s, got %s", tc.wantEndpoint, transportCreds.Endpoint)
 				}
 			}
 		})