ID Token Verification API (#3)

* ID token verification and unit tests

* Added documentation

* More documentation

* More documentation and cleanup

* Documentation

* Formatting changes

* Added a test case

* Code formatting changes

* Implementing signature verification as a LINQ query

* Separated FirebaseToken interface from impl; Added documentation

* Renamed IFirebaseToken back to FirebaseToken to stick with the approved API. Using FirebaseTokenArgs class to separate interface from impl

* Removed Uid from FirebaseTokenArgs

Author: hiranya911

FirebaseAdmin/FirebaseAdmin.Tests/Auth/FirebaseAuthTest.cs

@@ -0,0 +1,92 @@
+// Copyright 2018, Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Security.Cryptography;
+using System.Security.Cryptography.X509Certificates;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Xunit;
+using FirebaseAdmin.Auth;
+using Google.Apis.Auth;
+using Google.Apis.Auth.OAuth2;
+
+[assembly: CollectionBehavior(DisableTestParallelization = true)]
+namespace FirebaseAdmin.Auth.Tests
+{
+    public class FirebaseAuthTest: IDisposable
+    {
+        private static readonly GoogleCredential mockCredential =
+            GoogleCredential.FromAccessToken("test-token");
+
+        [Fact]
+        public void GetAuthWithoutApp()
+        {
+            Assert.Null(FirebaseAuth.DefaultInstance);
+        }
+
+        [Fact]
+        public void GetDefaultAuth()
+        {
+            var app = FirebaseApp.Create(new AppOptions(){Credential = mockCredential});
+            FirebaseAuth auth = FirebaseAuth.DefaultInstance;
+            Assert.Same(auth, FirebaseAuth.DefaultInstance);
+            app.Delete();
+            Assert.Null(FirebaseAuth.DefaultInstance);
+        }
+
+        [Fact]
+        public void GetAuth()
+        {
+            var app = FirebaseApp.Create(new AppOptions(){Credential = mockCredential}, "MyApp");
+            FirebaseAuth auth = FirebaseAuth.GetAuth(app);
+            Assert.Same(auth, FirebaseAuth.GetAuth(app));
+            app.Delete();
+            Assert.Throws<InvalidOperationException>(() => FirebaseAuth.GetAuth(app));
+        }
+
+        [Fact]
+        public async Task VerifyIdTokenNoProjectId()
+        {
+            FirebaseApp.Create(new AppOptions(){Credential = mockCredential});
+            var idToken = await FirebaseTokenVerifierTest.CreateTestTokenAsync();
+            await Assert.ThrowsAsync<ArgumentException>(
+                async () => await FirebaseAuth.DefaultInstance.VerifyIdTokenAsync(idToken));
+        }
+
+        [Fact]
+        public async Task VerifyIdTokenCancel()
+        {
+            FirebaseApp.Create(new AppOptions()
+            {
+                Credential = mockCredential,
+                ProjectId = "test-project",
+            });
+            var canceller = new CancellationTokenSource();
+            canceller.Cancel();
+            var idToken = await FirebaseTokenVerifierTest.CreateTestTokenAsync();
+            await Assert.ThrowsAsync<OperationCanceledException>(
+                async () => await FirebaseAuth.DefaultInstance.VerifyIdTokenAsync(
+                    idToken, canceller.Token));
+        }
+
+        public void Dispose()
+        {
+            FirebaseApp.DeleteAll();
+        }
+    }
+}