fix: Disable automatically retrieving Universe Domain from Metadata Server (#3272)

See internal ticket b/349488459 for more info.

External info:
ComputeEngineCredentials in client libraries should not validate the
universe domain. Validating the universe domain requires retrieving it
from Metadata Server (MDS) and this will be temporarily disabled.

For users that using client libraries, there will be no automatic call
to MDS. For users that use the Credentials directly and manually call
`ComputeEngineCredentials.getUniverseDomain()` and the universe domain
is not explicitly set, it will make a call to MDS.

Author: lqiu96

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

@@ -32,6 +32,7 @@
 import com.google.api.core.InternalApi;
 import com.google.api.gax.rpc.mtls.MtlsProvider;
 import com.google.auth.Credentials;
+import com.google.auth.oauth2.ComputeEngineCredentials;
 import com.google.auto.value.AutoValue;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Strings;
@@ -145,6 +146,11 @@ public void validateUniverseDomain(
       // GDC-H has no universe domain, return
       return;
     }
+    // (TODO: b/349488459) - Disable automatic requests to MDS until 01/2025
+    // If MDS is required for Universe Domain, do not do any validation
+    if (credentials instanceof ComputeEngineCredentials) {
+      return;
+    }
     String credentialsUniverseDomain = Credentials.GOOGLE_DEFAULT_UNIVERSE;
     // If credentials is not NoCredentialsProvider, use the Universe Domain inside Credentials
     if (credentials != null) {

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

@@ -29,12 +29,14 @@
  */
 package com.google.api.gax.rpc;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import com.google.api.gax.core.NoCredentialsProvider;
 import com.google.api.gax.rpc.mtls.MtlsProvider;
 import com.google.api.gax.rpc.testing.FakeMtlsProvider;
 import com.google.auth.Credentials;
+import com.google.auth.oauth2.ComputeEngineCredentials;
 import com.google.common.truth.Truth;
 import io.grpc.Status;
 import java.io.IOException;
@@ -437,4 +439,19 @@ void hasValidUniverseDomain_credentialsInGDU_configNonGDU() throws IOException {
         UnauthenticatedException.class,
         () -> endpointContext.validateUniverseDomain(credentials, statusCode));
   }
+
+  // (TODO: b/349488459) - Disable automatic requests to MDS until 01/2025
+  // Test is to ensure that no validation is being run for ComputeEngineCredentials
+  @Test
+  void hasValidUniverseDomain_computeEngineCredentials_noValidationOnUniverseDomain()
+      throws IOException {
+    Credentials credentials = Mockito.mock(ComputeEngineCredentials.class);
+    Mockito.when(credentials.getUniverseDomain()).thenReturn(Credentials.GOOGLE_DEFAULT_UNIVERSE);
+    EndpointContext endpointContext =
+        defaultEndpointContextBuilder
+            // Set a custom Universe Domain that doesn't match
+            .setUniverseDomain("test.com")
+            .build();
+    assertDoesNotThrow(() -> endpointContext.validateUniverseDomain(credentials, statusCode));
+  }
 }