title: Salesforce Authentication Failing
body: <p>I am trying to use OAuth authentication to get the Salesforce Authentication Token, so I referred <a href="http://wiki.developerforce.com/page/Digging_Deeper_into_OAuth_2.0_on_Force.com" rel="noreferrer">wiki docs</a>, but after getting authorization code, when I make a Post request with 5 required parameters, I'm getting following exception </p>
  
  <pre><code>{"error":"invalid_grant","error_description":"authentication failure"} CODE 400
  JSON = {"error":"invalid_grant","error_description":"authentication failure"}
  </code></pre>
  
  <p>which is I guess a bad request.</p>
  
  <pre><code>PostMethod post = new PostMethod("https://login.salesforce.com/services/oauth2/token");
  post.addParameter("code",##############);
  post.addParameter("grant_type","authorization_code");
  post.addParameter("redirect_uri","#################");  
  post.addParameter("client_id",this.client_id);
  post.addParameter("client_secret",this.client_secret);
  httpclient.executeMethod(post);
  String responseBody = post.getResponseBodyAsString();
  System.out.println(responseBody+" CODE "+post.getStatusCode());
  </code></pre>
  
  <p>Kindly reply, if exception known?</p>