docs: fix deprecation reference in ClientAuthInterceptor. (#2621)

auth/src/main/java/io/grpc/auth/ClientAuthInterceptor.java

@@ -58,7 +58,7 @@ import java.util.concurrent.Executor;
  * <p>Uses the new and simplified Google auth library:
  * https://github.com/google/google-auth-library-java
  *
- * @deprecated use {@link GoogleAuthLibraryCallCredentials} instead.
+ * @deprecated use {@link MoreCallCredentials#from(Credentials)} instead.
  */
 @Deprecated
 public final class ClientAuthInterceptor implements ClientInterceptor {

core/src/main/java/io/grpc/CallCredentials.java

@@ -37,6 +37,13 @@ import java.util.concurrent.Executor;
 
 /**
  * Carries credential data that will be propagated to the server via request metadata for each RPC.
+ *
+ * <p>This is used by {@link CallOptions#withCallCredentials} and {@code withCallCredentials()} on
+ * the generated stub, for example:
+ * <pre>
+ * FooGrpc.FooStub stub = FooGrpc.newStub(channel);
+ * response = stub.withCallCredentials(creds).bar(request);
+ * </pre>
  */
 @ExperimentalApi("https//github.com/grpc/grpc-java/issues/1914")
 public interface CallCredentials {