feat: GoogleCredential supports universe domain.

Src/Support/Google.Apis.Auth.Tests/OAuth2/GoogleCredentialTests.cs

@@ -272,6 +272,16 @@ public void FromStream_UserCredential()
             Assert.Equal("CLIENT_SECRET", flow.ClientSecrets.ClientSecret);
             Assert.Equal("PROJECT_ID", flow.ProjectId);
             Assert.Equal("QUOTA_PROJECT", userCred.QuotaProject);
+            Assert.Equal(GoogleAuthConsts.DefaultUniverseDomain, (userCred as IGoogleCredential).GetUniverseDomain());
+        }
+
+        [Fact]
+        public void CreateWithUniverseDomain_UserCredential_Fails()
+        {
+            var stream = new MemoryStream(Encoding.UTF8.GetBytes(FakeUserCredentialFileContents));
+            var credential = GoogleCredential.FromStream(stream);
+
+            Assert.Throws<InvalidOperationException>(() => credential.CreateWithUniverseDomain("fake.universe.domain.com"));
         }
 
         [Fact]
@@ -284,6 +294,24 @@ public void FromStream_ServiceAccountCredential()
             var serviceCred = (ServiceAccountCredential)credential.UnderlyingCredential;
             Assert.Equal("CLIENT_EMAIL", serviceCred.Id);
             Assert.Equal("PROJECT_ID", serviceCred.ProjectId);
+            Assert.Equal(GoogleAuthConsts.DefaultUniverseDomain, credential.GetUniverseDomain());
+        }
+
+        [Fact]
+        public void CreateWithUniverseDomain_ServiceAccountCredential()
+        {
+            var universeDomain = "fake.universe.domain.com";
+            var stream = new MemoryStream(Encoding.UTF8.GetBytes(FakeServiceAccountCredentialFileContents));
+            var credential = GoogleCredential.FromServiceAccountCredential(
+                ServiceAccountCredential.FromServiceAccountData(stream).WithUseJwtAccessWithScopes(true));
+
+            var newCredential = credential.CreateWithUniverseDomain(universeDomain);
+
+            Assert.NotSame(credential, newCredential);
+            Assert.IsType<ServiceAccountCredential>(newCredential.UnderlyingCredential);
+
+            Assert.Equal(GoogleAuthConsts.DefaultUniverseDomain, credential.GetUniverseDomain());
+            Assert.Equal(universeDomain, newCredential.GetUniverseDomain());
         }
 
         [Fact]

Src/Support/Google.Apis.Auth/OAuth2/GoogleCredential.cs

@@ -267,6 +267,37 @@ public static GoogleCredential FromComputeCredential(ComputeCredential computeCr
         /// </summary>
         public ICredential UnderlyingCredential => credential;
 
+        /// <summary>
+        /// Returns the universe domain this credential belongs to.
+        /// </summary>
+        /// <remarks>
+        /// For most credential types, this operation is synchronous and will always
+        /// return a completed task.
+        /// For <see cref="ComputeCredential"/>, the universe domain is obtained from the
+        /// metadata server, which requires an HTTP call. This value is obtained only once,
+        /// the first time it is requested for any instance of <see cref="ComputeCredential"/>.
+        /// After that, this method will always return a completed task.
+        /// The task's result will never be null.
+        /// </remarks>
+        public Task<string> GetUniverseDomainAsync(CancellationToken cancellationToken) =>
+            credential.GetUniverseDomainAsync(cancellationToken);
+
+        /// <summary>
+        /// Returns the universe domain this credential belongs to.
+        /// </summary>
+        /// <remarks>
+        /// Because <see cref="GetUniverseDomainAsync"/> is truly async only once, at most, in the lifetime
+        /// of an application, this method exists for convenience.
+        /// It can always be safely used for all credential types except for <see cref="ComputeCredential"/>.
+        /// For <see cref="ComputeCredential"/>, the universe domain is obtained from the
+        /// metadata server, which requires an HTTP call. This value is obtained only once,
+        /// the first time it is requested for any instance of <see cref="ComputeCredential"/>.
+        /// That first time, this method may block while waiting for the HTTP call to complete.
+        /// After that, this method will always be safe to use.
+        /// Will never return null.
+        /// </remarks>
+        public string GetUniverseDomain() => credential.GetUniverseDomain();
+
         /// <summary>
         /// If this library supports setting explicit scopes on this credential,
         /// this method will creates a copy of the credential with the specified scopes.
@@ -332,6 +363,16 @@ GoogleAuthConsts.EnvironmentQuotaProject is string environmentQuotaProject
         public virtual GoogleCredential CreateWithHttpClientFactory(IHttpClientFactory factory) =>
             new GoogleCredential(credential.WithHttpClientFactory(factory));
 
+        /// <summary>
+        /// If the credential supports custom universe domains this method will create a copy of the
+        /// credential with the specified universe domain set.
+        /// Otherwise, it throws <see cref="InvalidOperationException"/>.
+        /// </summary>
+        /// <param name="universeDomain">The universe domain to use for the credential.
+        /// May be null, in which case the default universe domain will be used.</param>
+        public GoogleCredential CreateWithUniverseDomain(string universeDomain) =>
+            new GoogleCredential(credential.WithUniverseDomain(universeDomain));
+
         void IConfigurableHttpClientInitializer.Initialize(ConfigurableHttpClient httpClient)
         {
             credential.Initialize(httpClient);