HttpClient handler with Auth using AAD

ActiveDirectoryAuthHandler.cs

	/// <summary>
	/// AuthHandler for AAD
	/// </summary>
	public class ActiveDirectoryAuthHandler : DelegatingHandler
	{
		private const int maxAuthRetry = 3;
		private readonly AuthenticationContext authContext;
		private readonly ClientCredential clientCredential;
		private readonly string appIdUri;

		public ActiveDirectoryAuthHandler(AuthenticationContext authContext
			, ClientCredential clientCredential
			, string appIdUri
			, HttpMessageHandler innerHandler) : base(innerHandler)
		{
			this.authContext = authContext ?? throw new ArgumentNullException(nameof(authContext));
			this.clientCredential = clientCredential ?? throw new ArgumentNullException(nameof(clientCredential));
			this.appIdUri = appIdUri ?? throw new ArgumentNullException(nameof(appIdUri));
		}

		public ActiveDirectoryAuthHandler(AuthenticationContext authContext
			, ClientCredential clientCredential
			, string appIdUri) : base(new HttpClientHandler())
		{
			this.authContext = authContext ?? throw new ArgumentNullException(nameof(authContext));
			this.clientCredential = clientCredential ?? throw new ArgumentNullException(nameof(clientCredential));
			this.appIdUri = appIdUri ?? throw new ArgumentNullException(nameof(appIdUri));
		}

		protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
		{
			var authResult = await GetAuth();
			if (authResult != null)
			{
				request.Headers.Authorization = new AuthenticationHeaderValue(authResult.AccessTokenType, authResult.AccessToken);
			}
			return await base.SendAsync(request, cancellationToken);
		}

		private async Task<AuthenticationResult> GetAuth()
		{
			int retryCount = 0;
			bool mustRetry;

			do
			{
				mustRetry = false;
				try
				{
					// ADAL includes an in memory cache, so this call will only send a message to the server if the cached token is expired.
					return await authContext.AcquireTokenAsync(appIdUri, clientCredential);
				}
				catch (AdalException ex) when (ex.ErrorCode == "temporarily_unavailable")
				{
					mustRetry = true;
					retryCount++;
					await Task.Delay(3000);
				}
			} while ((mustRetry == true) && (retryCount < maxAuthRetry));

			return null;
		}
	}

	public class ApiHttpClient
	{
		/// <summary>
		/// Create a new <see cref="HttpClient"/> with the <see cref="ActiveDirectoryAuthHandler"/> in the pipeline.
		/// </summary>
		/// <param name="aadInstance">The AAD-Instance (ex: https://login.microsoftonline.com/hunabku.onmicrosoft.com).</param>
		/// <param name="clientAppId">The App ID of this client.</param>
		/// <param name="clientAppKey">The App Key of this client.</param>
		/// <param name="apiAppIdUri">The App ID of the API</param>
		/// <param name="apiServerUrl">The API base address (ex: http://myapp.azurewebsites.net)</param>
		/// <returns>A new instance of <see cref="HttpClient"/>. </returns>
		public static HttpClient Default(string aadInstance
			, string clientAppId
			, string clientAppKey
			, string apiAppIdUri
			, string apiServerUrl = null)
		{
			var client = new HttpClient(new ActiveDirectoryAuthHandler(
				new AuthenticationContext(aadInstance)
				, new ClientCredential(clientAppId, clientAppKey)
				, apiAppIdUri));
			if (!string.IsNullOrWhiteSpace(apiServerUrl))
			{
				client.BaseAddress = new Uri(apiServerUrl);
			}

			return client;
		}

#if !NETSTANDARD
		/// <summary>
		/// Create a new <see cref="HttpClient"/> with the <see cref="ActiveDirectoryAuthHandler"/> and the <see cref="System.Net.Http.WebRequestHandler"/> in the pipeline.
		/// </summary>
		/// <param name="aadInstance">The AAD-Instance (ex: https://login.microsoftonline.com/hunabku.onmicrosoft.com).</param>
		/// <param name="clientAppId">The App ID of this client.</param>
		/// <param name="clientAppKey">The App Key of this client.</param>
		/// <param name="apiAppIdUri">The App ID of the API</param>
		/// <param name="apiServerUrl">The API base address (ex: http://myapp.azurewebsites.net)</param>
		/// <returns>A new instance of <see cref="HttpClient"/>. </returns>
		public static HttpClient WithNetCache(string aadInstance
			, string clientAppId
			, string clientAppKey
			, string apiAppIdUri
			, string apiServerUrl = null)
		{
			var client = new HttpClient(new ActiveDirectoryAuthHandler(
				new AuthenticationContext(aadInstance)
				, new ClientCredential(clientAppId, clientAppKey)
				, apiAppIdUri
				, new System.Net.Http.WebRequestHandler()
				{
					CachePolicy = new System.Net.Cache.HttpRequestCachePolicy(System.Net.Cache.HttpRequestCacheLevel.Default)
				}));
			if (!string.IsNullOrWhiteSpace(apiServerUrl))
			{
				client.BaseAddress = new Uri(apiServerUrl);
			}

			return client;
		}
#endif
	}