Connect to Microsoft Dynamics 365 web services using OAuth

บทความ
11/28/2016

Applies To: Dynamics 365 (online), Dynamics 365 (on-premises), Dynamics CRM 2016, Dynamics CRM Online

OAuth is the authentication method supported by the Microsoft Dynamics 365 Web API, and is one of two authentication methods for the Organization Service – the other being Active Directory authentication. One benefit of using OAuth is that your application can support multi-factor authentication. You can use OAuth authentication when your application connects to either the Organization service or the Discovery service.

Method calls to the web services must be authorized with the identity provider for that service endpoint. Authorization is approved when a valid OAuth 2.0 (user) access token, issued by Microsoft Azure Active Directory, is provided in the headers of the message requests.

The recommended authentication API for use with the Dynamics 365 Web API is Azure Active Directory Authentication Library (ADAL), which is available for a wide variety of platforms and programming languages. The ADAL API manages OAuth 2.0 authentication with the Dynamics 365 web service identity provider. For more details on the actual OAuth protocol used, see Use OAuth to Authenticate with the CRM Service.

Before you can use OAuth authentication to connect with the Dynamics 365 web services, your application must first be registered with Microsoft Azure Active Directory. Azure Active Directory is used to verify that your application is permitted access to the business data stored in a Dynamics 365 tenant.

Authenticate using ADAL

Basic OAuth web service authentication using ADAL is done using just a few lines of code.

// TODO Substitute your correct CRM root service address, 
string resource = "https://mydomain.crm.dynamics.com";

// TODO Substitute your app registration values that can be obtained after you
// register the app in Active Directory on the Microsoft Azure portal.
string clientId = "e5cf0024-a66a-4f16-85ce-99ba97a24bb2";
string redirectUrl = "https://localhost/SdkSample";


// Authenticate the registered application with Azure Active Directory.
AuthenticationContext authContext = 
    new AuthenticationContext("https://login.windows.net/common", false);
AuthenticationResult result = authContext.AcquireToken(resource, clientId, new
                                                       Uri(redirectUrl));

The authentication context is returned using a well-known authority provider. When you don’t know the Azure Active Directory tenant associated with the Dynamics 365 instance you’re calling, you can use a constant string of " https://login.windows.net/common", which is the authority URL for a multiple tenant scenario. An alternate method to dynamically discover the authority at run time is described later in this topic.

The next line of code gets the authentication result that contains the access token you’re looking for. You can send message requests to the web service with this token.

A few more items of interest in this code are the string values used. The resource variable contains the Transport Layer Security (TLS) or Secure Sockets Layer (SSL) root address, including the domain (organization), of your Dynamics 365 server. The clientId and redirectUrl variables contain the app registration information that is the result of registering the app with Active Directory. For more information on app registration, see Walkthrough: Register a Dynamics 365 app with Azure Active Directory.

Use the access token in message requests

Depending on the Dynamics 365 API you’re using, there are two different methods to send a message request to the web services. For the Web API, you would typically send an HTTP message request. For the Organization Service, you would send a message request using the web client proxy.

HTTP message request

Once you have the access token, you must set the Authorization header of the message request that you are sending to the web service to the access token value and specify the token type of “ Bearer”. For more information on the Authorization header, see section 14.8 of the HTTP/1.1 protocol. The following code demonstrates how this is done using the System.Net.Http.HttpClient class.

using (HttpClient httpClient = new HttpClient())
{
    httpClient.Timeout = new TimeSpan(0, 2, 0);  // 2 minutes
    httpClient.DefaultRequestHeaders.Authorization = 
        new AuthenticationHeaderValue("Bearer", result.AccessToken);

Web client requests

Simply set the HeaderToken property value to the access token when using OrganizationWebProxyClient or DiscoveryWebProxyClient of the Organization Service.

Refresh the access token

It’s a recommended best practice to refresh the access token before each call to a Dynamics 365 web service method. This is a workaround to writing code that checks the access token expiration date and time and refreshes the token when it’s about to expire.

To refresh the access token, which is cached by ADAL, you simply call the AcquireToken method again using the same context.

AuthenticationResult result = authContext.AcquireToken(resource, clientId, new Uri(redirectUrl));

Afterwards, you once again set the Authorization header with result.AccessToken when using the Web API, or the HeaderToken when using the Organization Service.

httpClient.DefaultRequestHeaders.Authorization = 
    new AuthenticationHeaderValue("Bearer", result.AccessToken);

Discover the authority at run time

The authentication authority URL, and the resource URL, can be determined dynamically at run time using the following ADAL code. This is the recommended method to use as compared to the well-known authority URL shown previously in a code snippet.

AuthenticationParameters ap = AuthenticationParameters.CreateFromResourceUrlAsync(
                        new Uri("https://mydomain.crm.dynamics.com/api/data/")).Result;

String authorityUrl = ap.Authority;
String resourceUrl  = ap.Resource;

For the Web API, another way to obtain the authority URL is to send any message request to the web service specifying no access token. This is known as a bearer challenge. The response can be parsed to obtain the authority URL.

httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", “”);

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