title: refresh_token Invalid Credentials errors
body: <p>I'm stumped. I'm trying to manually get a refresh token to load an access token for me on Mirror API using Perl and it keeps giving me credentials errors. When I load the exact HTTP request in the PHP example code (I've printed out the HTTP to compare) the same refresh_token works fine.</p>
  
  <p>Here's my Perl HTTP request:</p>
  
  <p>*POST <a href="https://accounts.google.com/o/oauth2/token" rel="nofollow">https://accounts.google.com/o/oauth2/token</a>
  Host: accounts.google.com
  User-Agent: libwww-perl/6.02
  Content-Length: 175
  Content-Type: application/x-www-form-urlencoded
  client_id=client_id_goes_here&amp;client_secret=client_secret_goes_here&amp;refresh_token=refresh_token_goes_here&amp;grant_type=refresh_token*</p>
  
  <p>Here's the PHP on the same refresh_token:</p>
  
  <p>*POST /o/oauth2/token HTTP/1.1
  content-type: application/x-www-form-urlencoded
  content-length: 175
  client_id=client_id_goes_here&amp;client_secret=client_secret_goes_here&amp;refresh_token=refresh_token_goes_here&amp;grant_type=refresh_token*</p>
  
  <p>My Perl looks like this:</p>
  
  <pre><code>my $auth_response = $ua-&gt;request(POST 'https://accounts.google.com/o/oauth2/token',
              'Host'          =&gt; 'accounts.google.com',
              'Content_Type'  =&gt; 'application/x-www-form-urlencoded',
              'Content'       =&gt; [
                  'client_id'         =&gt;  $client_id,
                  'client_secret'     =&gt;  $client_secret,
                  'refresh_token'     =&gt;  $credentials-&gt;{'refresh_token'},
                  'grant_type'        =&gt;  'refresh_token',
              ],
          );
  </code></pre>
  
  <p>HELP! :-)</p>