title: invalid_grant when using grant type "authorization_code"
body: <p>Hi I am getting an error of "invalid_grant" when trying to use a grant_type of "authorization_code".</p>
  
  <p>Here is the url I use for the OAuth2 authorization endpoint:
  <a href="https://soundcloud.com/connect?client_id=myClientId&amp;redirect_uri=http://www.bing.com&amp;response_type=code&amp;scope=non-expiring" rel="nofollow">https://soundcloud.com/connect?client_id=myClientId&amp;redirect_uri=http://www.bing.com&amp;response_type=code&amp;scope=non-expiring</a></p>
  
  <p>Here is my message body for the OAuth2 token endpoint:</p>
  
  <pre><code>Dictionary&lt;string, string&gt; messageBody = new Dictionary&lt;string, string&gt;();
  messageBody.Add("client_id", clientId);
  messageBody.Add("client_secret", clientSecret);
  messageBody.Add("redirect_uri", "http://www.bing.com");
  messageBody.Add("grant_type", "authorization_code");
  messageBody.Add("code", code);
  </code></pre>
  
  <p>Any help is much appreciated!</p>