examples: add an example to illustrate authorization (authz) support

examples/examples_test.sh

@@ -52,6 +52,7 @@ EXAMPLES=(
     "helloworld"
     "route_guide"
     "features/authentication"
+    "features/authz"
     "features/cancellation"
     "features/compression"
     "features/deadline"
@@ -101,6 +102,7 @@ declare -A EXPECTED_SERVER_OUTPUT=(
     ["helloworld"]="Received: world"
     ["route_guide"]=""
     ["features/authentication"]="server starting on port 50051..."
+    ["features/authz"]="unary echoing message \"hello world\""
     ["features/cancellation"]="server: error receiving from stream: rpc error: code = Canceled desc = context canceled"
     ["features/compression"]="UnaryEcho called with message \"compress\""
     ["features/deadline"]=""
@@ -120,6 +122,7 @@ declare -A EXPECTED_CLIENT_OUTPUT=(
     ["helloworld"]="Greeting: Hello world"
     ["route_guide"]="Feature: name: \"\", point:(416851321, -742674555)"
     ["features/authentication"]="UnaryEcho:  hello world"
+    ["features/authz"]="UnaryEcho:  hello world"
     ["features/cancellation"]="cancelling context"
     ["features/compression"]="UnaryEcho call returned \"compress\", <nil>"
     ["features/deadline"]="wanted = DeadlineExceeded, got = DeadlineExceeded"

examples/features/authz/README.md

@@ -0,0 +1,16 @@
+# RBAC authorization
+
+This example uses the `StaticInterceptor` from the `google.golang.org/grpc/authz` package.
+It uses a header based RBAC policy to match each gRPC method to a required role. For simplicity,
+the context is injected with mock metadata which includes the required roles, but this should
+be fetched from an appropriate service based on the authenticated context.
+
+## Try it
+
+```
+go run server/main.go
+```
+
+```
+go run client/main.go
+```

examples/features/authz/client/main.go

@@ -0,0 +1,132 @@
+/*
+ *
+ * Copyright 2023 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Binary client is an example client.
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"time"
+
+	"golang.org/x/oauth2"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/credentials/oauth"
+	"google.golang.org/grpc/examples/data"
+	"google.golang.org/grpc/examples/features/authz/token"
+	ecpb "google.golang.org/grpc/examples/features/proto/echo"
+	"google.golang.org/grpc/status"
+)
+
+var addr = flag.String("addr", "localhost:50051", "the address to connect to")
+
+func callUnaryEcho(ctx context.Context, client ecpb.EchoClient, message string, opts ...grpc.CallOption) error {
+	resp, err := client.UnaryEcho(ctx, &ecpb.EchoRequest{Message: message}, opts...)
+	if err != nil {
+		return status.Errorf(status.Code(err), "UnaryEcho RPC failed: %v", err)
+	}
+	fmt.Println("UnaryEcho: ", resp.Message)
+	return nil
+}
+
+func callBidiStreamingEcho(ctx context.Context, client ecpb.EchoClient, opts ...grpc.CallOption) error {
+	c, err := client.BidirectionalStreamingEcho(ctx, opts...)
+	if err != nil {
+		return status.Errorf(status.Code(err), "BidirectionalStreamingEcho RPC failed: %v", err)
+	}
+	for i := 0; i < 5; i++ {
+		if err := c.Send(&ecpb.EchoRequest{Message: fmt.Sprintf("Request %d", i+1)}); err != nil {
+			return status.Errorf(status.Code(err), "sending StreamingEcho message: %v", err)
+		}
+	}
+	c.CloseSend()
+	for {
+		resp, err := c.Recv()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return status.Errorf(status.Code(err), "receiving StreamingEcho message: %v", err)
+		}
+		fmt.Println("BidiStreaming Echo: ", resp.Message)
+	}
+	return nil
+}
+
+func newCredentialsCallOption(t token.Token) grpc.CallOption {
+	tokenBase64, err := t.Encode()
+	if err != nil {
+		log.Fatalf("encoding token: %v", err)
+	}
+	oath2Token := oauth2.Token{AccessToken: tokenBase64}
+	return grpc.PerRPCCredentials(oauth.TokenSource{TokenSource: oauth2.StaticTokenSource(&oath2Token)})
+}
+
+func main() {
+	flag.Parse()
+
+	// Create tls based credential.
+	creds, err := credentials.NewClientTLSFromFile(data.Path("x509/ca_cert.pem"), "x.test.example.com")
+	if err != nil {
+		log.Fatalf("failed to load credentials: %v", err)
+	}
+	// Set up a connection to the server.
+	conn, err := grpc.Dial(*addr, grpc.WithTransportCredentials(creds))
+	if err != nil {
+		log.Fatalf("grpc.Dial(%q): %v", *addr, err)
+	}
+	defer conn.Close()
+
+	// Make an echo client and send RPCs.
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+	client := ecpb.NewEchoClient(conn)
+
+	// Make RPCs as an authorized user and expect them to succeed.
+	authorisedUserTokenCallOption := newCredentialsCallOption(token.Token{Username: "super-user", Secret: "super-secret"})
+	if err := callUnaryEcho(ctx, client, "hello world", authorisedUserTokenCallOption); err != nil {
+		log.Fatalf("Unary RPC by authorized user failed: %v", err)
+	}
+	if err := callBidiStreamingEcho(ctx, client, authorisedUserTokenCallOption); err != nil {
+		log.Fatalf("Bidirectional RPC by authorized user failed: %v", err)
+	}
+
+	// Make RPCs as an unauthorized user and expect them to fail with status code PermissionDenied.
+	unauthorisedUserTokenCallOption := newCredentialsCallOption(token.Token{Username: "bad-actor", Secret: "super-secret"})
+	if err := callUnaryEcho(ctx, client, "hello world", unauthorisedUserTokenCallOption); err != nil {
+		switch c := status.Code(err); c {
+		case codes.PermissionDenied:
+			log.Printf("Unary RPC by unauthorized user failed as expected: %v", err)
+		default:
+			log.Fatalf("Unary RPC by unauthorized user failed unexpectedly: %v, %v", c, err)
+		}
+	}
+	if err := callBidiStreamingEcho(ctx, client, unauthorisedUserTokenCallOption); err != nil {
+		switch c := status.Code(err); c {
+		case codes.PermissionDenied:
+			log.Printf("Bidirectional RPC by unauthorized user failed as expected: %v", err)
+		default:
+			log.Fatalf("Bidirectional RPC by unauthorized user failed unexpectedly: %v", err)
+		}
+	}
+}

examples/features/authz/server/main.go

@@ -0,0 +1,215 @@
+/*
+ *
+ * Copyright 2023 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Binary server is an example server.
+package main
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"strings"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/authz"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/examples/data"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/status"
+
+	"google.golang.org/grpc/examples/features/authz/token"
+	pb "google.golang.org/grpc/examples/features/proto/echo"
+)
+
+const (
+	unaryEchoWriterRole      = "UNARY_ECHO:W"
+	streamEchoReadWriterRole = "STREAM_ECHO:RW"
+	authzPolicy              = `
+	{
+		"name": "authz",
+		"allow_rules": [
+			{
+				"name": "allow_UnaryEcho",
+				"request": {
+					"paths": ["/grpc.examples.echo.Echo/UnaryEcho"],
+					"headers": [
+						{
+							"key": "UNARY_ECHO:W",
+							"values": ["true"]
+						}
+					]
+				}
+			},
+			{
+				"name": "allow_BidirectionalStreamingEcho",
+				"request": {
+					"paths": ["/grpc.examples.echo.Echo/BidirectionalStreamingEcho"],
+					"headers": [
+						{
+							"key": "STREAM_ECHO:RW",
+							"values": ["true"]
+						}
+					]
+				}
+			}
+		],
+		"deny_rules": []
+	}
+	`
+)
+
+var (
+	port = flag.Int("port", 50051, "the port to serve on")
+
+	errMissingMetadata = status.Errorf(codes.InvalidArgument, "missing metadata")
+)
+
+func newContextWithRoles(ctx context.Context, username string) context.Context {
+	md := metadata.MD{}
+	if username == "super-user" {
+		md.Set(unaryEchoWriterRole, "true")
+		md.Set(streamEchoReadWriterRole, "true")
+	}
+	return metadata.NewIncomingContext(ctx, md)
+}
+
+type server struct {
+	pb.UnimplementedEchoServer
+}
+
+func (s *server) UnaryEcho(ctx context.Context, in *pb.EchoRequest) (*pb.EchoResponse, error) {
+	fmt.Printf("unary echoing message %q\n", in.Message)
+	return &pb.EchoResponse{Message: in.Message}, nil
+}
+
+func (s *server) BidirectionalStreamingEcho(stream pb.Echo_BidirectionalStreamingEchoServer) error {
+	for {
+		in, err := stream.Recv()
+		if err != nil {
+			if err == io.EOF {
+				return nil
+			}
+			fmt.Printf("Receiving message from stream: %v\n", err)
+			return err
+		}
+		fmt.Printf("bidi echoing message %q\n", in.Message)
+		stream.Send(&pb.EchoResponse{Message: in.Message})
+	}
+}
+
+// isAuthenticated validates the authorization.
+func isAuthenticated(authorization []string) (username string, err error) {
+	if len(authorization) < 1 {
+		return "", errors.New("received empty authorization token from client")
+	}
+	tokenBase64 := strings.TrimPrefix(authorization[0], "Bearer ")
+	// Perform the token validation here. For the sake of this example, the code
+	// here forgoes any of the usual OAuth2 token validation and instead checks
+	// for a token matching an arbitrary string.
+	var token token.Token
+	err = token.Decode(tokenBase64)
+	if err != nil {
+		return "", fmt.Errorf("base64 decoding of received token %q: %v", tokenBase64, err)
+	}
+	if token.Secret != "super-secret" {
+		return "", fmt.Errorf("received token %q does not match expected %q", token.Secret, "super-secret")
+	}
+	return token.Username, nil
+}
+
+// authUnaryInterceptor looks up the authorization header from the incoming RPC context,
+// retrieves the username from it and creates a new context with the username before invoking
+// the provided handler.
+func authUnaryInterceptor(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
+	md, ok := metadata.FromIncomingContext(ctx)
+	if !ok {
+		return nil, errMissingMetadata
+	}
+	username, err := isAuthenticated(md["authorization"])
+	if err != nil {
+		return nil, status.Error(codes.Unauthenticated, err.Error())
+	}
+	return handler(newContextWithRoles(ctx, username), req)
+}
+
+// wrappedStream wraps a grpc.ServerStream associated with an incoming RPC, and
+// a custom context containing the username derived from the authorization header
+// specified in the incoming RPC metadata
+type wrappedStream struct {
+	grpc.ServerStream
+	ctx context.Context
+}
+
+func (w *wrappedStream) Context() context.Context {
+	return w.ctx
+}
+
+func newWrappedStream(ctx context.Context, s grpc.ServerStream) grpc.ServerStream {
+	return &wrappedStream{s, ctx}
+}
+
+// authStreamInterceptor looks up the authorization header from the incoming RPC context,
+// retrieves the username from it and creates a new context with the username before invoking
+// the provided handler.
+func authStreamInterceptor(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
+	md, ok := metadata.FromIncomingContext(ss.Context())
+	if !ok {
+		return errMissingMetadata
+	}
+	username, err := isAuthenticated(md["authorization"])
+	if err != nil {
+		return status.Error(codes.Unauthenticated, err.Error())
+	}
+	return handler(srv, newWrappedStream(newContextWithRoles(ss.Context(), username), ss))
+}
+
+func main() {
+	flag.Parse()
+
+	lis, err := net.Listen("tcp", fmt.Sprintf(":%d", *port))
+	if err != nil {
+		log.Fatalf("Listening on local port %q: %v", *port, err)
+	}
+
+	// Create tls based credential.
+	creds, err := credentials.NewServerTLSFromFile(data.Path("x509/server_cert.pem"), data.Path("x509/server_key.pem"))
+	if err != nil {
+		log.Fatalf("Loading credentials: %v", err)
+	}
+
+	// Create an authorization interceptor using a static policy.
+	staticInteceptor, err := authz.NewStatic(authzPolicy)
+	if err != nil {
+		log.Fatalf("Creating a static authz interceptor: %v", err)
+	}
+	unaryInts := grpc.ChainUnaryInterceptor(authUnaryInterceptor, staticInteceptor.UnaryInterceptor)
+	streamInts := grpc.ChainStreamInterceptor(authStreamInterceptor, staticInteceptor.StreamInterceptor)
+	s := grpc.NewServer(grpc.Creds(creds), unaryInts, streamInts)
+
+	// Register EchoServer on the server.
+	pb.RegisterEchoServer(s, &server{})
+
+	if err := s.Serve(lis); err != nil {
+		log.Fatalf("Serving Echo service on local port: %v", err)
+	}
+}