feat: Validate the Universe Domain

[lqiu96]

Universe Domain validation ensures that the user configured value matches the one set in the Credentials. If validation does not succeed, the call should not proceed. Validating the unvierse domain should occur prior to each RPC invocation.

Behavior shared between transports:

• Try to validate the credentials. If universe domain matches, proceed with the call. Otherwise, return an Unauthorized exception back to the user.

Transport Specific Behavior:

• gRPC: If the Credentials is unable to get the universe domain due to an Auth Exception, mark the exception as Unavailable and retry the call following the retry bounds defined by the RPC. Otherwise, return the exception back to the user.
• HttpJson: If the Credentials is unable to get the universe domain due to an Auth Exception, return the exception back to the user.

CallContext's merge()

Callables are created with the TransportCallableFactory using the defaultCallContext. The defaultCallContext is merged with the call's callcontext in a default invocation:

sdk-platform-java/gax-java/gax/src/main/java/com/google/api/gax/rpc/UnaryCallable.java

Line 126 in 97ae228

return UnaryCallable.this.futureCall(request, defaultCallContext.merge(thisCallContext));

GAPIC clients expose callables which invoke the call() with a null callcontext: https://github.com/googleapis/google-cloud-java/blob/c12ae4aacc597161211d53f15c60d6ab904d19d2/java-accessapproval/google-cloud-accessapproval/src/main/java/com/google/cloud/accessapproval/v1/AccessApprovalAdminClient.java#L701-L703.
Merge is not invoked and does not result in creating the EndpointContext over and over again.

[sonarqubecloud]

Quality Gate failed for 'gapic-generator-java-root'

Failed conditions

52.9% Coverage on New Code (required ≥ 80%)

See analysis details on SonarCloud

[sonarqubecloud]

Quality Gate failed for 'java_showcase_integration_tests'

Failed conditions

51.4% Coverage on New Code (required ≥ 80%)

See analysis details on SonarCloud