feat: Add experimental S2A integration in client libraries grpc transport

gapic-generator-java-pom-parent/pom.xml

@@ -27,7 +27,7 @@
         consistent across modules in this repository -->
     <javax.annotation-api.version>1.3.2</javax.annotation-api.version>
     <grpc.version>1.68.1</grpc.version>
-    <google.auth.version>1.29.0</google.auth.version>
+    <google.auth.version>1.29.1-SNAPSHOT</google.auth.version>
     <google.http-client.version>1.45.0</google.http-client.version>
     <gson.version>2.11.0</gson.version>
     <guava.version>33.3.1-jre</guava.version>

gax-java/gax-grpc/BUILD.bazel

@@ -28,6 +28,7 @@ _COMPILE_DEPS = [
     "@io_grpc_grpc_netty_shaded//jar",
     "@io_grpc_grpc_grpclb//jar",
     "@io_grpc_grpc_java//alts:alts",
+    "@io_grpc_grpc_java//s2a:s2a",
     "@io_netty_netty_tcnative_boringssl_static//jar",
     "@javax_annotation_javax_annotation_api//jar",
     "//gax:gax",

gax-java/gax-grpc/pom.xml

@@ -63,6 +63,10 @@
       <groupId>io.grpc</groupId>
       <artifactId>grpc-protobuf</artifactId>
     </dependency>
+    <dependency>
+      <groupId>io.grpc</groupId>
+      <artifactId>grpc-s2a</artifactId>
+    </dependency>
     <dependency>
       <groupId>io.grpc</groupId>
       <artifactId>grpc-stub</artifactId>

gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProvider.java

@@ -37,6 +37,7 @@
 import com.google.api.core.InternalApi;
 import com.google.api.core.ObsoleteApi;
 import com.google.api.gax.core.ExecutorProvider;
+import com.google.api.gax.rpc.EndpointContext;
 import com.google.api.gax.rpc.FixedHeaderProvider;
 import com.google.api.gax.rpc.HeaderProvider;
 import com.google.api.gax.rpc.TransportChannel;
@@ -46,21 +47,28 @@
 import com.google.auth.ApiKeyCredentials;
 import com.google.auth.Credentials;
 import com.google.auth.oauth2.ComputeEngineCredentials;
+import com.google.auth.oauth2.S2A;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
+import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.io.Files;
 import io.grpc.CallCredentials;
 import io.grpc.ChannelCredentials;
 import io.grpc.Grpc;
+import io.grpc.InsecureChannelCredentials;
 import io.grpc.ManagedChannel;
 import io.grpc.ManagedChannelBuilder;
 import io.grpc.TlsChannelCredentials;
 import io.grpc.alts.GoogleDefaultChannelCredentials;
 import io.grpc.auth.MoreCallCredentials;
+import io.grpc.s2a.S2AChannelCredentials;
 import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
 import java.io.IOException;
+import java.io.InputStream;
 import java.nio.charset.StandardCharsets;
 import java.security.GeneralSecurityException;
 import java.security.KeyStore;
@@ -99,6 +107,11 @@ public final class InstantiatingGrpcChannelProvider implements TransportChannelP
   @VisibleForTesting
   static final String DIRECT_PATH_ENV_ENABLE_XDS = "GOOGLE_CLOUD_ENABLE_DIRECT_PATH_XDS";
 
+  private static final String MTLS_MDS_ROOT = "/run/google-mds-mtls/root.crt";
+  // The mTLS MDS credentials are formatted as the concatenation of a PEM-encoded certificate chain
+  // followed by a PEM-encoded private key.
+  private static final String MTLS_MDS_CERT_CHAIN_AND_KEY = "/run/google-mds-mtls/client.key";
+
   static final long DIRECT_PATH_KEEP_ALIVE_TIME_SECONDS = 3600;
   static final long DIRECT_PATH_KEEP_ALIVE_TIMEOUT_SECONDS = 20;
   static final String GCE_PRODUCTION_NAME_PRIOR_2016 = "Google";
@@ -107,6 +120,7 @@ public final class InstantiatingGrpcChannelProvider implements TransportChannelP
   private final int processorCount;
   private final Executor executor;
   private final HeaderProvider headerProvider;
+  private final EndpointContext endpointContext;
   private final String endpoint;
   // TODO: remove. envProvider currently provides DirectPath environment variable, and is only used
   // during initial rollout for DirectPath. This provider will be removed once the DirectPath
@@ -136,6 +150,7 @@ private InstantiatingGrpcChannelProvider(Builder builder) {
     this.executor = builder.executor;
     this.headerProvider = builder.headerProvider;
     this.endpoint = builder.endpoint;
+    this.endpointContext = builder.endpointContext;
     this.mtlsProvider = builder.mtlsProvider;
     this.envProvider = builder.envProvider;
     this.interceptorProvider = builder.interceptorProvider;
@@ -225,6 +240,17 @@ public TransportChannelProvider withEndpoint(String endpoint) {
     return toBuilder().setEndpoint(endpoint).build();
   }
 
+  /**
+   * Specify the {@link EndpointContext}.
+   *
+   * @param endpointContext
+   * @return A new {@link InstantiatingGrpcChannelProvider} with the endpointContext
+   */
+  @Override
+  public TransportChannelProvider withEndpointContext(EndpointContext endpointContext) {
+    return toBuilder().setEndpointContext(endpointContext).build();
+  }
+
   /** @deprecated Please modify pool settings via {@link #toBuilder()} */
   @Deprecated
   @Override
@@ -410,6 +436,80 @@ ChannelCredentials createMtlsChannelCredentials() throws IOException, GeneralSec
     return null;
   }
 
+  @VisibleForTesting
+  ChannelCredentials createMtlsToS2AChannelCredentials(
+      InputStream trustBundle, InputStream privateKey, InputStream certChain) throws IOException {
+    if (trustBundle == null || privateKey == null || certChain == null) {
+      return null;
+    }
+    return TlsChannelCredentials.newBuilder()
+        .keyManager(privateKey, certChain)
+        .trustManager(trustBundle)
+        .build();
+  }
+
+  ChannelCredentials createPlaintextToS2AChannelCredentials(String plaintextAddress) {
+    if (Strings.isNullOrEmpty(plaintextAddress)) {
+      return null;
+    }
+    return S2AChannelCredentials.newBuilder(plaintextAddress, InsecureChannelCredentials.create())
+        .build();
+  }
+
+  /**
+   * This method creates gRPC {@link ChannelCredentials} configured to use S2A to estbalish a mTLS
+   * connection. First, the address of S2A is discovered by using the {@link S2A} utility to learn
+   * the {@code mtlsAddress} to reach S2A and the {@code plaintextAddress} to reach S2A. Prefer to
+   * use the {@code mtlsAddress} address to reach S2A if it is non-empty and the MTLS-MDS
+   * credentials can successfully be discovered and used to create {@link TlsChannelCredentials}. If
+   * there is any failure using mTLS-to-S2A, fallback to using a plaintext connection to S2A using
+   * the {@code plaintextAddress}.
+   *
+   * @return {@link ChannelCredentials} configured to use S2A to create mTLS connection to
+   *     mtlsEndpoint.
+   */
+  ChannelCredentials createS2ASecuredChannelCredentials() {
+    S2A s2aUtils = S2A.newBuilder().build();
+    String plaintextAddress = s2aUtils.getPlaintextS2AAddress();
+    String mtlsAddress = s2aUtils.getMtlsS2AAddress();
+    if (Strings.isNullOrEmpty(mtlsAddress)) {
+      // Fallback to plaintext connection to S2A.
+      return createPlaintextToS2AChannelCredentials(plaintextAddress);
+    }
+    // Currently, MTLS to MDS is only available on GCE. See:
+    // https://cloud.google.com/compute/docs/metadata/overview#https-mds
+    // Try to load MTLS-MDS creds.
+    InputStream trustBundle = null;
+    InputStream privateKey = null;
+    InputStream certChain = null;
+    try {
+      trustBundle = new FileInputStream(MTLS_MDS_ROOT);
+      privateKey = new FileInputStream(MTLS_MDS_CERT_CHAIN_AND_KEY);
+      certChain = new FileInputStream(MTLS_MDS_CERT_CHAIN_AND_KEY);
+    } catch (FileNotFoundException ignore) {
+      // Fallback to plaintext-to-S2A connection.
+      LOG.log(
+          Level.INFO,
+          "Cannot establish an mTLS connection to S2A due to error loading MTLS to MDS credentials, falling back to plaintext connection to S2A: "
+              + ignore.getMessage());
+      return createPlaintextToS2AChannelCredentials(plaintextAddress);
+    }
+    ChannelCredentials mtlsToS2AChannelCredentials = null;
+    try {
+      // Try to connect to S2A using mTLS.
+      mtlsToS2AChannelCredentials =
+          createMtlsToS2AChannelCredentials(trustBundle, privateKey, certChain);
+    } catch (IOException ignore) {
+      // Fallback to plaintext-to-S2A connection.
+      LOG.log(
+          Level.INFO,
+          "Cannot establish an mTLS connection to S2A due to error creating MTLS to MDS TlsChannelCredentials credentials, falling back to plaintext connection to S2A: "
+              + ignore.getMessage());
+      return createPlaintextToS2AChannelCredentials(plaintextAddress);
+    }
+    return S2AChannelCredentials.newBuilder(mtlsAddress, mtlsToS2AChannelCredentials).build();
+  }
+
   private ManagedChannel createSingleChannel() throws IOException {
     GrpcHeaderInterceptor headerInterceptor =
         new GrpcHeaderInterceptor(headersWithDuplicatesRemoved);
@@ -447,16 +547,30 @@ private ManagedChannel createSingleChannel() throws IOException {
       builder.keepAliveTime(DIRECT_PATH_KEEP_ALIVE_TIME_SECONDS, TimeUnit.SECONDS);
       builder.keepAliveTimeout(DIRECT_PATH_KEEP_ALIVE_TIMEOUT_SECONDS, TimeUnit.SECONDS);
     } else {
+      // Try and create credentials via DCA. See https://google.aip.dev/auth/4114.
       ChannelCredentials channelCredentials;
       try {
         channelCredentials = createMtlsChannelCredentials();
       } catch (GeneralSecurityException e) {
         throw new IOException(e);
       }
       if (channelCredentials != null) {
+        // Create the channel using channel credentials created via DCA.
         builder = Grpc.newChannelBuilder(endpoint, channelCredentials);
       } else {
-        builder = ManagedChannelBuilder.forAddress(serviceAddress, port);
+        // Could not create channel credentials via DCA. In accordance with
+        // https://google.aip.dev/auth/4115, if credentials not available through
+        // DCA, try mTLS with credentials held by the S2A (Secure Session Agent).
+        if (endpointContext.useS2A()) {
+          channelCredentials = createS2ASecuredChannelCredentials();
+        }
+        if (channelCredentials != null) {
+          // Create the channel using S2A-secured channel credentials.
+          builder = Grpc.newChannelBuilder(endpointContext.mtlsEndpoint(), channelCredentials);
+        } else {
+          // Use default if we cannot initialize channel credentials via DCA or S2A.
+          builder = ManagedChannelBuilder.forAddress(serviceAddress, port);
+        }
       }
     }
     // google-c2p resolver requires service config lookup
@@ -604,6 +718,7 @@ public static final class Builder {
     private Executor executor;
     private HeaderProvider headerProvider;
     private String endpoint;
+    private EndpointContext endpointContext;
     private EnvironmentProvider envProvider;
     private MtlsProvider mtlsProvider = new MtlsProvider();
     @Nullable private GrpcInterceptorProvider interceptorProvider;
@@ -632,6 +747,7 @@ private Builder(InstantiatingGrpcChannelProvider provider) {
       this.executor = provider.executor;
       this.headerProvider = provider.headerProvider;
       this.endpoint = provider.endpoint;
+      this.endpointContext = provider.endpointContext;
       this.envProvider = provider.envProvider;
       this.interceptorProvider = provider.interceptorProvider;
       this.maxInboundMessageSize = provider.maxInboundMessageSize;
@@ -700,6 +816,11 @@ public Builder setEndpoint(String endpoint) {
       return this;
     }
 
+    Builder setEndpointContext(EndpointContext endpointContext) {
+      this.endpointContext = endpointContext;
+      return this;
+    }
+
     @VisibleForTesting
     Builder setMtlsProvider(MtlsProvider mtlsProvider) {
       this.mtlsProvider = mtlsProvider;

gax-java/gax-grpc/src/test/java/com/google/api/gax/grpc/GrpcLongRunningTest.java

@@ -101,6 +101,8 @@ void setUp() throws IOException {
     TransportChannel transportChannel =
         GrpcTransportChannel.newBuilder().setManagedChannel(channel).build();
     when(operationsChannelProvider.getTransportChannel()).thenReturn(transportChannel);
+    when(operationsChannelProvider.withEndpointContext(Mockito.any(EndpointContext.class)))
+        .thenReturn(operationsChannelProvider);
 
     clock = new FakeApiClock(0L);
     executor = RecordingScheduler.create(clock);