src/csharp/Grpc.Auth/OAuth2Interceptors.cs

#region Copyright notice and license

// Copyright 2015, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
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#endregion

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Security.Cryptography.X509Certificates;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;

using Google.Apis.Auth.OAuth2;
using Google.Apis.Util;
using Grpc.Core;
using Grpc.Core.Utils;

namespace Grpc.Auth
{
    public static class OAuth2Interceptors
    {
        /// <summary>
        /// Creates OAuth2 interceptor that will obtain access token from GoogleCredentials.
        /// </summary>
        public static MetadataInterceptorDelegate FromCredential(GoogleCredential googleCredential)
        {
            var interceptor = new OAuth2Interceptor(googleCredential.InternalCredential, SystemClock.Default);
            return new MetadataInterceptorDelegate(interceptor.InterceptHeaders);
        }

        /// <summary>
        /// Creates OAuth2 interceptor that will use given OAuth2 token.
        /// </summary>
        /// <param name="oauth2Token"></param>
        /// <returns></returns>
        public static MetadataInterceptorDelegate FromAccessToken(string oauth2Token)
        {
            Preconditions.CheckNotNull(oauth2Token);
            return new MetadataInterceptorDelegate((metadata) =>
            {
                metadata.Add(OAuth2Interceptor.CreateBearerTokenHeader(oauth2Token));
            });
        }

        /// <summary>
        /// Injects OAuth2 authorization header into initial metadata (= request headers).
        /// </summary>
        private class OAuth2Interceptor
        {
            private const string AuthorizationHeader = "Authorization";
            private const string Schema = "Bearer";

            private ServiceCredential credential;
            private IClock clock;

            public OAuth2Interceptor(ServiceCredential credential, IClock clock)
            {
                this.credential = credential;
                this.clock = clock;
            }

            /// <summary>
            /// Gets access token and requests refreshing it if is going to expire soon.
            /// </summary>
            /// <param name="cancellationToken"></param>
            /// <returns></returns>
            public string GetAccessToken(CancellationToken cancellationToken)
            {
                if (credential.Token == null || credential.Token.IsExpired(clock))
                {
                    // TODO(jtattermusch): Parallel requests will spawn multiple requests to refresh the token once the token expires.
                    // TODO(jtattermusch): Rethink synchronous wait to obtain the result.
                    if (!credential.RequestAccessTokenAsync(cancellationToken).Result)
                    {
                        throw new InvalidOperationException("The access token has expired but we can't refresh it");
                    }
                }
                return credential.Token.AccessToken;
            }

            public void InterceptHeaders(Metadata metadata)
            {
                var accessToken = GetAccessToken(CancellationToken.None);
                metadata.Add(CreateBearerTokenHeader(accessToken));
            }

            public static Metadata.Entry CreateBearerTokenHeader(string accessToken)
            {
                return new Metadata.Entry(AuthorizationHeader, Schema + " " + accessToken);
            }
        }
    }
}