How to use OAuth2 in RestSharp

See RFC 6749 – 4.4.2. Client Credentials – Access Token Request

Here is the basic format of the request

POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded

grant_type=client_credentials

Your cURL request

curl -H "Accept: application/json" \
     -d grant_type=client_credentials \
     client-app:[email protected]/myapi/oauth/token 

The reason your cURL command works

1. Default Content-Type (if not specified) with POST (default when you use -d switch) is application/x-www-form-urlencoded

2. Default authentication type, if not specified, is Basic. The username and password are passed either through the -u option or in the URL

    -u username:password (client-app:secret)
   
    -- or put it in the url --
   
    client-app:[email protected]/myapi/oauth/token
   

   You could also specify the auth type with --basic or --digest

You can use the -v switch in your cURL command to see all the headers involved in the request.

RestSharp fix:

1. Set the Content-Type to application/x-www-form-urlencoded

2. Add the Basic authentication

    client.Authenticator = new HttpBasicAuthenticator("client-app", "secret");
   

3. Get rid of

    request.AddParameter("client_id", "client-app");
    request.AddParameter("client_secret", "secret");
   

4. Set the Accept header to application/json