How to obtain an OAuth access token in Dynamics CRM 365 Online using C#

The following code snippet demonstrates how to obtain an OAuth access token from your Dynamics CRM online instance that you can use to pass as authenticated and authorization when accessing Dynamics CRM 365 web services in your client-side or server-side code.

using (HttpClient client = new HttpClient())
{
   client.BaseAddress = new 
       Uri("https://login.microsoftonline.com/common/oauth2/token");

   HttpRequestMessage request = new HttpRequestMessage();
   request.Method = HttpMethod.Post;

   var keysValues = new List<KeyValuePair<string, string>>();
   keysValues.Add(new KeyValuePair<string, string>("client_id", 
       "2ad88395-b77d-4561-9441-d0e40824f9bc"));
   keysValues.Add(new KeyValuePair<string, string>("resource", url));
   keysValues.Add(new KeyValuePair<string, string>("username", username));
   keysValues.Add(new KeyValuePair<string, string>("password", password));
   keysValues.Add(new KeyValuePair<string, string>("grant_type", "password"));

   request.Content = new FormUrlEncodedContent(keysValues);

   HttpResponseMessage response = client.SendAsync(request).Result;
   return response.StatusCode == HttpStatusCode.OK;
}

In the code snippet above, the only thing that will change are username and password, there are your Dynamics 365 credentials to authenticate and authorize your instance, also the URL for your Dynamics CRM instance (e.g. https://benjsoftdemo.crm3.dynamics.com).

The client_id is the default Client Id which is setup against Dynamics 365 Online instances.

You can test the following code snippet using Postman.

When successful, the response will contain the JSON response payload that contains your access_token.

Then you can use the access_token programmatically to authenticate and authorize you when accessing the CRM webservice calls.

For more information, you can refer to the following link Dynamics 365 Online Authenticate with User Credentials.