Add support for new setAllowHardBoundTokens field.

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

@@ -64,6 +64,7 @@
 import java.nio.charset.StandardCharsets;
 import java.security.GeneralSecurityException;
 import java.security.KeyStore;
+import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -126,6 +127,7 @@ public final class InstantiatingGrpcChannelProvider implements TransportChannelP
   @Nullable private final Boolean allowNonDefaultServiceAccount;
   @VisibleForTesting final ImmutableMap<String, ?> directPathServiceConfig;
   @Nullable private final MtlsProvider mtlsProvider;
+  @Nullable private final ArrayList<String> allowedValues;
   @VisibleForTesting final Map<String, String> headersWithDuplicatesRemoved = new HashMap<>();
 
   @Nullable
@@ -136,6 +138,7 @@ private InstantiatingGrpcChannelProvider(Builder builder) {
     this.executor = builder.executor;
     this.headerProvider = builder.headerProvider;
     this.endpoint = builder.endpoint;
+    this.allowedValues = builder.allowedValues;
     this.mtlsProvider = builder.mtlsProvider;
     this.envProvider = builder.envProvider;
     this.interceptorProvider = builder.interceptorProvider;
@@ -225,6 +228,11 @@ public TransportChannelProvider withEndpoint(String endpoint) {
     return toBuilder().setEndpoint(endpoint).build();
   }
 
+  @Override
+  public TransportChannelProvider setAllowHardBoundTokens(ArrayList<String> allowedValues) {
+    return toBuilder().setAllowHardBoundTokens(allowedValues).build();
+  }
+
   /** @deprecated Please modify pool settings via {@link #toBuilder()} */
   @Deprecated
   @Override
@@ -620,6 +628,7 @@ public static final class Builder {
     @Nullable private Boolean attemptDirectPathXds;
     @Nullable private Boolean allowNonDefaultServiceAccount;
     @Nullable private ImmutableMap<String, ?> directPathServiceConfig;
+    @Nullable private ArrayList<String> allowedValues;
 
     private Builder() {
       processorCount = Runtime.getRuntime().availableProcessors();
@@ -700,6 +709,11 @@ public Builder setEndpoint(String endpoint) {
       return this;
     }
 
+    public Builder setAllowHardBoundTokens(ArrayList<String> allowedValues) {
+      this.allowedValues = allowedValues;
+      return this;
+    }
+
     @VisibleForTesting
     Builder setMtlsProvider(MtlsProvider mtlsProvider) {
       this.mtlsProvider = mtlsProvider;

gax-java/gax-grpc/src/test/java/com/google/api/gax/grpc/testing/LocalChannelProvider.java

@@ -47,6 +47,7 @@
 import io.grpc.MethodDescriptor;
 import io.grpc.inprocess.InProcessChannelBuilder;
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.CopyOnWriteArrayList;
@@ -106,6 +107,12 @@ public TransportChannelProvider withEndpoint(String endpoint) {
     throw new UnsupportedOperationException("LocalChannelProvider doesn't need an endpoint");
   }
 
+  @Override
+  public TransportChannelProvider setAllowHardBoundTokens(ArrayList<String> allowedValues) {
+    throw new UnsupportedOperationException(
+        "LocalChannelProvider doesn't support hard-bound tokens");
+  }
+
   @Override
   @BetaApi("The surface for customizing pool size is not stable yet and may change in the future.")
   public boolean acceptsPoolSize() {

gax-java/gax-httpjson/src/main/java/com/google/api/gax/httpjson/InstantiatingHttpJsonChannelProvider.java

@@ -42,6 +42,7 @@
 import java.io.IOException;
 import java.security.GeneralSecurityException;
 import java.security.KeyStore;
+import java.util.ArrayList;
 import java.util.Map;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ScheduledExecutorService;
@@ -139,6 +140,12 @@ public TransportChannelProvider withPoolSize(int size) {
         "InstantiatingHttpJsonChannelProvider doesn't allow pool size customization");
   }
 
+  @Override
+  public TransportChannelProvider setAllowHardBoundTokens(ArrayList<String> allowedValues) {
+    throw new UnsupportedOperationException(
+        "InstantiatingHttpJsonChannelProvider doesn't support hard-bound tokens");
+  }
+
   @Override
   public String getTransportName() {
     return HttpJsonTransportChannel.getHttpJsonTransportName();

gax-java/gax/src/main/java/com/google/api/gax/rpc/FixedTransportChannelProvider.java

@@ -33,6 +33,7 @@
 import com.google.auth.Credentials;
 import com.google.common.base.Preconditions;
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Map;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ScheduledExecutorService;
@@ -68,6 +69,12 @@ public FixedTransportChannelProvider withExecutor(Executor executor) {
         "FixedTransportChannelProvider doesn't need an executor");
   }
 
+  @Override
+  public TransportChannelProvider setAllowHardBoundTokens(ArrayList<String> allowedValues) {
+    throw new UnsupportedOperationException(
+        "FixedTransportChannelProvider doesn't support hard-bound tokens");
+  }
+
   @Override
   public boolean needsHeaders() {
     return false;

gax-java/gax/src/main/java/com/google/api/gax/rpc/TransportChannelProvider.java

@@ -33,6 +33,7 @@
 import com.google.api.core.InternalExtensionOnly;
 import com.google.auth.Credentials;
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Map;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ScheduledExecutorService;
@@ -97,6 +98,9 @@ public interface TransportChannelProvider {
    */
   TransportChannelProvider withEndpoint(String endpoint);
 
+  /** Sets the allowed hard bound token types. */
+  TransportChannelProvider setAllowHardBoundTokens(ArrayList<String> allowedValues);
+
   /**
    * Reports whether this provider allows pool size customization.
    *

gax-java/gax/src/test/java/com/google/api/gax/rpc/ClientContextTest.java

@@ -63,6 +63,7 @@
 import com.google.common.truth.Truth;
 import java.io.IOException;
 import java.net.URI;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -200,6 +201,17 @@ public boolean acceptsPoolSize() {
       return false;
     }
 
+    @Override
+    public TransportChannelProvider setAllowHardBoundTokens(ArrayList<String> allowedValues) {
+      return new FakeTransportProvider(
+          this.transport,
+          this.executor,
+          this.shouldAutoClose,
+          this.headers,
+          this.credentials,
+          this.endpoint);
+    }
+
     @Override
     public TransportChannelProvider withPoolSize(int size) {
       throw new UnsupportedOperationException(