feat: add support for new setAllowHardBoundTokens field.

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

@@ -126,6 +126,7 @@ public final class InstantiatingGrpcChannelProvider implements TransportChannelP
   @Nullable private final Boolean allowNonDefaultServiceAccount;
   @VisibleForTesting final ImmutableMap<String, ?> directPathServiceConfig;
   @Nullable private final MtlsProvider mtlsProvider;
+  @Nullable private final List<String> allowedHardBoundTokenTypes;
   @VisibleForTesting final Map<String, String> headersWithDuplicatesRemoved = new HashMap<>();
 
   @Nullable
@@ -136,6 +137,7 @@ private InstantiatingGrpcChannelProvider(Builder builder) {
     this.executor = builder.executor;
     this.headerProvider = builder.headerProvider;
     this.endpoint = builder.endpoint;
+    this.allowedHardBoundTokenTypes = builder.allowedHardBoundTokenTypes;
     this.mtlsProvider = builder.mtlsProvider;
     this.envProvider = builder.envProvider;
     this.interceptorProvider = builder.interceptorProvider;
@@ -620,6 +622,7 @@ public static final class Builder {
     @Nullable private Boolean attemptDirectPathXds;
     @Nullable private Boolean allowNonDefaultServiceAccount;
     @Nullable private ImmutableMap<String, ?> directPathServiceConfig;
+    @Nullable private List<String> allowedHardBoundTokenTypes;
 
     private Builder() {
       processorCount = Runtime.getRuntime().availableProcessors();
@@ -700,6 +703,12 @@ public Builder setEndpoint(String endpoint) {
       return this;
     }
 
+    @InternalApi
+    public Builder setAllowHardBoundTokenTypes(List<String> allowedValues) {
+      this.allowedHardBoundTokenTypes = allowedValues;
+      return this;
+    }
+
     @VisibleForTesting
     Builder setMtlsProvider(MtlsProvider mtlsProvider) {
       this.mtlsProvider = mtlsProvider;