title: how to use request.AddParameter(restsharp) in HttpClient
body: <p>i have this code and worked</p>
  
  <pre><code>string userName = "username";
          string password = "password";
          string clientSecret = "clientSecretCode";
          var client = new RestClient("url");
          var request = new RestRequest(Method.POST);
          request.AddHeader("Content-Type", "application/x-www-form-urlencoded");
          request.AddParameter("undefined",
              $"grant_type=password&amp;username={userName}&amp;password={password}&amp;client_id=mmp-web-api&amp;client_secret={clientSecret}&amp;scope=openid%20mmp-webpanel",
              ParameterType.RequestBody);
          IRestResponse response = client.Execute(request);
          var result = JsonConvert.DeserializeObject&lt;TokenOutputDto&gt;(response.Content);
  </code></pre>
  
  <p>TokenOutputDto is :</p>
  
  <pre><code>public class TokenOutputDto
  {
      public string access_token { get; set; }
  }
  </code></pre>
  
  <p>how i can convert this code to httpclient(run without RestSharp)</p>