Polishing of C# auth API

src/csharp/Grpc.Auth/GoogleAuthInterceptors.cs

@@ -41,10 +41,10 @@ using Grpc.Core.Utils;
 namespace Grpc.Auth
 {
     /// <summary>
-    /// Factory methods to create authorization interceptors.
-    /// <seealso cref="GrpcCredentials"/>
+    /// Factory methods to create authorization interceptors for Google credentials.
+    /// <seealso cref="GoogleGrpcCredentials"/>
     /// </summary>
-    public static class AuthInterceptors
+    public static class GoogleAuthInterceptors
     {
         private const string AuthorizationHeader = "Authorization";
         private const string Schema = "Bearer";

src/csharp/Grpc.Auth/GoogleGrpcCredentials.cs

@@ -33,6 +33,7 @@
 
 using System;
 using System.Threading;
+using System.Threading.Tasks;
 
 using Google.Apis.Auth.OAuth2;
 using Grpc.Core;
@@ -41,53 +42,55 @@ using Grpc.Core.Utils;
 namespace Grpc.Auth
 {
     /// <summary>
-    /// Factory methods to create instances of <see cref="ChannelCredentials"/> and <see cref="CallCredentials"/> classes.
+    /// Factory/extension methods to create instances of <see cref="ChannelCredentials"/> and <see cref="CallCredentials"/> classes
+    /// based on credential objects originating from Google auth library.
     /// </summary>
-    public static class GrpcCredentials
+    public static class GoogleGrpcCredentials
     {
         /// <summary>
-        /// Creates a <see cref="MetadataCredentials"/> instance that will obtain access tokens 
-        /// from any credential that implements <c>ITokenAccess</c>. (e.g. <c>GoogleCredential</c>).
+        /// Retrieves an instance of Google's Application Default Credentials using
+        /// <c>GoogleCredential.GetApplicationDefaultAsync()</c> and converts them
+        /// into a gRPC <see cref="ChannelCredentials"/> that use the default SSL credentials.
         /// </summary>
-        /// <param name="credential">The credential to use to obtain access tokens.</param>
-        /// <returns>The <c>MetadataCredentials</c> instance.</returns>
-        public static MetadataCredentials Create(ITokenAccess credential)
+        /// <returns>The <c>ChannelCredentials</c> instance.</returns>
+        public static async Task<ChannelCredentials> GetApplicationDefaultAsync()
         {
-            return new MetadataCredentials(AuthInterceptors.FromCredential(credential));
+            var googleCredential = await GoogleCredential.GetApplicationDefaultAsync().ConfigureAwait(false);
+            return googleCredential.ToChannelCredentials();
         }
 
         /// <summary>
-        /// Convenience method to create a <see cref="ChannelCredentials"/> instance from
-        /// <c>ITokenAccess</c> credential and <c>SslCredentials</c> instance.
+        /// Creates an instance of <see cref="CallCredentials"/> that will use given access token to authenticate
+        /// with a gRPC service.
         /// </summary>
-        /// <param name="credential">The credential to use to obtain access tokens.</param>
-        /// <param name="sslCredentials">The <c>SslCredentials</c> instance.</param>
-        /// <returns>The channel credentials for access token based auth over a secure channel.</returns>
-        public static ChannelCredentials Create(ITokenAccess credential, SslCredentials sslCredentials)
+        /// <param name="accessToken">OAuth2 access token.</param>
+        /// /// <returns>The <c>MetadataCredentials</c> instance.</returns>
+        public static CallCredentials FromAccessToken(string accessToken)
         {
-            return ChannelCredentials.Create(sslCredentials, Create(credential));
+            return CallCredentials.FromInterceptor(GoogleAuthInterceptors.FromAccessToken(accessToken));
         }
 
         /// <summary>
-        /// Creates an instance of <see cref="MetadataCredentials"/> that will use given access token to authenticate
-        /// with a gRPC service.
+        /// Converts a <c>ITokenAccess</c> (e.g. <c>GoogleCredential</c>) object
+        /// into a gRPC <see cref="CallCredentials"/> object.
         /// </summary>
-        /// <param name="accessToken">OAuth2 access token.</param>
-        /// /// <returns>The <c>MetadataCredentials</c> instance.</returns>
-        public static MetadataCredentials FromAccessToken(string accessToken)
+        /// <param name="credential">The credential to use to obtain access tokens.</param>
+        /// <returns>The <c>CallCredentials</c> instance.</returns>
+        public static CallCredentials ToCallCredentials(this ITokenAccess credential)
         {
-            return new MetadataCredentials(AuthInterceptors.FromAccessToken(accessToken));
+            return CallCredentials.FromInterceptor(GoogleAuthInterceptors.FromCredential(credential));
         }
 
         /// <summary>
-        /// Converts a <c>ITokenAccess</c> object into a <see cref="MetadataCredentials"/> object supported
-        /// by gRPC.
+        /// Converts a <c>ITokenAccess</c> (e.g. <c>GoogleCredential</c>) object
+        /// into a gRPC <see cref="ChannelCredentials"/> object.
+        /// Default SSL credentials are used.
         /// </summary>
-        /// <param name="credential"></param>
-        /// <returns></returns>
-        public static MetadataCredentials ToGrpcCredentials(this ITokenAccess credential)
+        /// <param name="googleCredential">The credential to use to obtain access tokens.</param>
+        /// <returns>>The <c>ChannelCredentials</c> instance.</returns>
+        public static ChannelCredentials ToChannelCredentials(this ITokenAccess googleCredential)
         {
-            return GrpcCredentials.Create(credential);
+            return ChannelCredentials.Create(new SslCredentials(), googleCredential.ToCallCredentials());
         }
     }
 }

src/csharp/Grpc.Auth/Grpc.Auth.csproj

@@ -78,9 +78,9 @@
     <Compile Include="..\Grpc.Core\Version.cs">
       <Link>Version.cs</Link>
     </Compile>
-    <Compile Include="GrpcCredentials.cs" />
+    <Compile Include="GoogleGrpcCredentials.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
-    <Compile Include="AuthInterceptors.cs" />
+    <Compile Include="GoogleAuthInterceptors.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <ItemGroup>

src/csharp/Grpc.Core.Tests/CallCredentialsTest.cs

@@ -55,8 +55,8 @@ namespace Grpc.Core.Tests
         public void CallCredentials_ToNativeCredentials()
         {
             var composite = CallCredentials.Compose(
-                new MetadataCredentials(async (uri, m) => { await Task.Delay(1); }),
-                new MetadataCredentials(async (uri, m) => { await Task.Delay(2); }));
+                CallCredentials.FromInterceptor(async (uri, m) => { await Task.Delay(1); }),
+                CallCredentials.FromInterceptor(async (uri, m) => { await Task.Delay(2); }));
             using (var nativeComposite = composite.ToNativeCredentials())
             {
             }

src/csharp/Grpc.Core.Tests/ChannelCredentialsTest.cs

@@ -63,11 +63,5 @@ namespace Grpc.Core.Tests
             // forbid composing non-composable
             Assert.Throws(typeof(ArgumentException), () => ChannelCredentials.Create(new FakeChannelCredentials(false), new FakeCallCredentials()));
         }
-
-        [Test]
-        public void ChannelCredentials_CreateWrapped()
-        {
-            ChannelCredentials.Create(new FakeCallCredentials());
-        }
     }
 }

src/csharp/Grpc.Core/CallCredentials.cs

@@ -40,6 +40,14 @@ using Grpc.Core.Utils;
 
 namespace Grpc.Core
 {
+    /// <summary>
+    /// Asynchronous authentication interceptor for <see cref="CallCredentials"/>.
+    /// </summary>
+    /// <param name="authUri">URL of a service to which current remote call needs to authenticate</param>
+    /// <param name="metadata">Metadata to populate with entries that will be added to outgoing call's headers.</param>
+    /// <returns></returns>
+    public delegate Task AsyncAuthInterceptor(string authUri, Metadata metadata);
+
     /// <summary>
     /// Client-side call credentials. Provide authorization with per-call granularity.
     /// </summary>
@@ -56,6 +64,16 @@ namespace Grpc.Core
             return new CompositeCallCredentials(credentials);
         }
 
+        /// <summary>
+        /// Creates a new instance of <c>CallCredentials</c> class from an
+        /// interceptor that can attach metadata to outgoing calls.
+        /// </summary>
+        /// <param name="interceptor">authentication interceptor</param>
+        public static CallCredentials FromInterceptor(AsyncAuthInterceptor interceptor)
+        {
+            return new MetadataCredentials(interceptor);
+        }
+
         /// <summary>
         /// Creates native object for the credentials.
         /// </summary>
@@ -63,19 +81,11 @@ namespace Grpc.Core
         internal abstract CredentialsSafeHandle ToNativeCredentials();
     }
 
-    /// <summary>
-    /// Asynchronous authentication interceptor for <see cref="MetadataCredentials"/>.
-    /// </summary>
-    /// <param name="authUri">URL of a service to which current remote call needs to authenticate</param>
-    /// <param name="metadata">Metadata to populate with entries that will be added to outgoing call's headers.</param>
-    /// <returns></returns>
-    public delegate Task AsyncAuthInterceptor(string authUri, Metadata metadata);
-
     /// <summary>
     /// Client-side credentials that delegate metadata based auth to an interceptor.
     /// The interceptor is automatically invoked for each remote call that uses <c>MetadataCredentials.</c>
     /// </summary>
-    public class MetadataCredentials : CallCredentials
+    internal sealed class MetadataCredentials : CallCredentials
     {
         readonly AsyncAuthInterceptor interceptor;
 
@@ -85,7 +95,7 @@ namespace Grpc.Core
         /// <param name="interceptor">authentication interceptor</param>
         public MetadataCredentials(AsyncAuthInterceptor interceptor)
         {
-            this.interceptor = interceptor;
+            this.interceptor = Preconditions.CheckNotNull(interceptor);
         }
 
         internal override CredentialsSafeHandle ToNativeCredentials()

src/csharp/Grpc.Core/ChannelCredentials.cs

@@ -71,17 +71,6 @@ namespace Grpc.Core
             return new CompositeChannelCredentials(channelCredentials, callCredentials);
         }
 
-        /// <summary>
-        /// Creates a new instance of <c>ChannelCredentials</c> by wrapping
-        /// an instance of <c>CallCredentials</c>.
-        /// </summary>
-        /// <param name="callCredentials">Call credentials.</param>
-        /// <returns>The <c>ChannelCredentials</c> wrapping given call credentials.</returns>
-        public static ChannelCredentials Create(CallCredentials callCredentials)
-        {
-            return new WrappedCallCredentials(callCredentials);
-        }
-
         /// <summary>
         /// Creates native object for the credentials. May return null if insecure channel
         /// should be created.
@@ -213,26 +202,4 @@ namespace Grpc.Core
             }
         }
     }
-
-    /// <summary>
-    /// Credentials wrapping <see cref="CallCredentials"/> as <see cref="ChannelCredentials"/>.
-    /// </summary>
-    internal sealed class WrappedCallCredentials : ChannelCredentials
-    {
-        readonly CallCredentials callCredentials;
-
-        /// <summary>
-        /// Wraps instance of <c>CallCredentials</c> as <c>ChannelCredentials</c>.
-        /// </summary>
-        /// <param name="callCredentials">credentials to wrap</param>
-        public WrappedCallCredentials(CallCredentials callCredentials)
-        {
-            this.callCredentials = Preconditions.CheckNotNull(callCredentials);
-        }
-
-        internal override CredentialsSafeHandle ToNativeCredentials()
-        {
-            return callCredentials.ToNativeCredentials();
-        }
-    }
 }

src/csharp/Grpc.IntegrationTesting/InteropClient.cs

@@ -143,14 +143,14 @@ namespace Grpc.IntegrationTesting
             {
                 var googleCredential = await GoogleCredential.GetApplicationDefaultAsync();
                 Assert.IsTrue(googleCredential.IsCreateScopedRequired);
-                credentials = ChannelCredentials.Create(credentials, googleCredential.ToGrpcCredentials());
+                credentials = ChannelCredentials.Create(credentials, googleCredential.ToCallCredentials());
             }
 
             if (options.TestCase == "compute_engine_creds")
             {
                 var googleCredential = await GoogleCredential.GetApplicationDefaultAsync();
                 Assert.IsFalse(googleCredential.IsCreateScopedRequired);
-                credentials = ChannelCredentials.Create(credentials, googleCredential.ToGrpcCredentials());
+                credentials = ChannelCredentials.Create(credentials, googleCredential.ToCallCredentials());
             }
             return credentials;
         }
@@ -392,7 +392,7 @@ namespace Grpc.IntegrationTesting
             ITokenAccess credential = (await GoogleCredential.GetApplicationDefaultAsync()).CreateScoped(new[] { oauthScope });
             string oauth2Token = await credential.GetAccessTokenForRequestAsync();
 
-            var credentials = GrpcCredentials.FromAccessToken(oauth2Token);
+            var credentials = GoogleGrpcCredentials.FromAccessToken(oauth2Token);
             var request = new SimpleRequest
             {
                 FillUsername = true,
@@ -412,7 +412,7 @@ namespace Grpc.IntegrationTesting
             Console.WriteLine("running per_rpc_creds");
             ITokenAccess googleCredential = await GoogleCredential.GetApplicationDefaultAsync();
 
-            var credentials = GrpcCredentials.Create(googleCredential);
+            var credentials = googleCredential.ToCallCredentials();
             var request = new SimpleRequest
             {
                 FillUsername = true,

src/csharp/Grpc.IntegrationTesting/MetadataCredentialsTest.cs

@@ -75,7 +75,7 @@ namespace Grpc.IntegrationTesting
 
             var clientCredentials = ChannelCredentials.Create(
                 new SslCredentials(File.ReadAllText(TestCredentials.ClientCertAuthorityPath)),
-                new MetadataCredentials(asyncAuthInterceptor));
+                CallCredentials.FromInterceptor(asyncAuthInterceptor));
             channel = new Channel(Host, server.Ports.Single().BoundPort, clientCredentials, options);
             client = TestService.NewClient(channel);
         }