Add service_account_creds test.

Fixes #456

Manually tested with ./run-test-client.sh --server_port=443 --server_host=grpc-test.sandbox.google.com --server_host_override=grpc-test.sandbox.google.com --service_account_key_file=/usr/local/google/home/simonma/gce_cred.json --oauth_scope=https://www.googleapis.com/auth/xapi.zoo --test_case=service_account_creds

interop-testing/src/main/java/io/grpc/testing/integration/AbstractTransportTest.java

@@ -43,6 +43,8 @@ import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoMoreInteractions;
 
 import com.google.auth.oauth2.ComputeEngineCredentials;
+import com.google.auth.oauth2.GoogleCredentials;
+import com.google.auth.oauth2.ServiceAccountCredentials;
 import com.google.protobuf.ByteString;
 import com.google.protobuf.EmptyProtos.Empty;
 
@@ -68,7 +70,6 @@ import io.grpc.testing.integration.Messages.StreamingInputCallRequest;
 import io.grpc.testing.integration.Messages.StreamingInputCallResponse;
 import io.grpc.testing.integration.Messages.StreamingOutputCallRequest;
 import io.grpc.testing.integration.Messages.StreamingOutputCallResponse;
-
 import org.junit.After;
 import org.junit.Assert;
 import org.junit.Before;
@@ -76,6 +77,7 @@ import org.junit.Test;
 import org.mockito.ArgumentCaptor;
 
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.Arrays;
 import java.util.List;
 import java.util.concurrent.ArrayBlockingQueue;
@@ -632,6 +634,43 @@ public abstract class AbstractTransportTest {
     verifyNoMoreInteractions(responseObserver);
   }
 
+  /** Sends a large unary rpc with service account credentials. */
+  public void serviceAccountCreds(String jsonKey, InputStream credentialsStream, String authScope)
+      throws Exception {
+    // cast to ServiceAccountCredentials to double-check the right type of object was created.
+    GoogleCredentials credentials =
+        (ServiceAccountCredentials) GoogleCredentials.fromStream(credentialsStream);
+    credentials = credentials.createScoped(Arrays.<String>asList(authScope));
+    TestServiceGrpc.TestServiceBlockingStub stub = blockingStub.configureNewStub()
+        .addInterceptor(new ClientAuthInterceptor(credentials, testServiceExecutor))
+        .build();
+    final SimpleRequest request = SimpleRequest.newBuilder()
+        .setFillUsername(true)
+        .setFillOauthScope(true)
+        .setResponseSize(314159)
+        .setResponseType(PayloadType.COMPRESSABLE)
+        .setPayload(Payload.newBuilder()
+            .setBody(ByteString.copyFrom(new byte[271828])))
+        .build();
+
+    final SimpleResponse response = stub.unaryCall(request);
+    assertFalse(response.getUsername().isEmpty());
+    assertTrue("Received username: " + response.getUsername(),
+        jsonKey.contains(response.getUsername()));
+    assertFalse(response.getOauthScope().isEmpty());
+    assertTrue("Received oauth scope: " + response.getOauthScope(),
+        authScope.contains(response.getOauthScope()));
+
+    final SimpleResponse goldenResponse = SimpleResponse.newBuilder()
+        .setOauthScope(response.getOauthScope())
+        .setUsername(response.getUsername())
+        .setPayload(Payload.newBuilder()
+            .setType(PayloadType.COMPRESSABLE)
+            .setBody(ByteString.copyFrom(new byte[314159])))
+        .build();
+    assertEquals(goldenResponse, response);
+  }
+
   /** Sends a large unary rpc with compute engine credentials. */
   public void computeEngineCreds(String serviceAccount, String oauthScope) throws Exception {
     ComputeEngineCredentials credentials = new ComputeEngineCredentials();

interop-testing/src/main/java/io/grpc/testing/integration/TestServiceClient.java

@@ -31,6 +31,8 @@
 
 package io.grpc.testing.integration;
 
+import com.google.common.io.Files;
+
 import io.grpc.ChannelImpl;
 import io.grpc.testing.TestUtils;
 import io.grpc.transport.netty.GrpcSslContexts;
@@ -39,9 +41,12 @@ import io.grpc.transport.netty.NettyChannelBuilder;
 import io.grpc.transport.okhttp.OkHttpChannelBuilder;
 import io.netty.handler.ssl.SslContext;
 
+import java.io.File;
+import java.io.FileInputStream;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.UnknownHostException;
+import java.nio.charset.Charset;
 
 import javax.net.ssl.SSLSocketFactory;
 
@@ -85,6 +90,7 @@ public class TestServiceClient {
   private boolean useTestCa;
   private boolean useOkHttp;
   private String defaultServiceAccount;
+  private String serviceAccountKeyFile;
   private String oauthScope;
 
   private Tester tester = new Tester();
@@ -131,6 +137,8 @@ public class TestServiceClient {
         }
       } else if ("default_service_account".equals(key)) {
         defaultServiceAccount = value;
+      } else if ("service_account_key_file".equals(key)) {
+        serviceAccountKeyFile = value;
       } else if ("oauth_scope".equals(key)) {
         oauthScope = value;
       } else {
@@ -152,9 +160,11 @@ public class TestServiceClient {
           + "\n  --use_tls=true|false        Whether to use TLS. Default " + c.useTls
           + "\n  --use_test_ca=true|false    Whether to trust our fake CA. Default " + c.useTestCa
           + "\n  --use_okhttp=true|false     Whether to use OkHttp instead of Netty. Default "
-              + c.useOkHttp
+            + c.useOkHttp
           + "\n  --default_service_account   Email of GCE default service account. Default "
-              + c.defaultServiceAccount
+            + c.defaultServiceAccount
+          + "\n  --service_account_key_file  Path to service account json key file."
+            + c.serviceAccountKeyFile
           + "\n  --oauth_scope               Scope for OAuth tokens. Default " + c.oauthScope
       );
       System.exit(1);
@@ -206,6 +216,10 @@ public class TestServiceClient {
       tester.cancelAfterFirstResponse();
     } else if ("compute_engine_creds".equals(testCase)) {
       tester.computeEngineCreds(defaultServiceAccount, oauthScope);
+    } else if ("service_account_creds".equals(testCase)) {
+      String jsonKey = Files.toString(new File(serviceAccountKeyFile), Charset.forName("UTF-8"));
+      FileInputStream credentialsStream = new FileInputStream(new File(serviceAccountKeyFile));
+      tester.serviceAccountCreds(jsonKey, credentialsStream, oauthScope);
     } else {
       throw new IllegalArgumentException("Unknown test case: " + testCase);
     }