title: Clickbank api not authenticating
body: <p>Despite of assigning right API key and Dev key click bank does not authenticate my application to authenticate. It rturns 403 forbidden message.</p>
  
  <p>What is the wrong with my script?</p>
  
  <pre><code> $ch = curl_init();
      curl_setopt($ch, CURLOPT_URL, "https://api.clickbank.com/rest/1.2/sandbox/validateDeveloperKey");
      curl_setopt($ch, CURLOPT_HEADER, true); 
      curl_setopt($ch, CURLOPT_GET, true);
      curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
  
  //for security reasons these are not real keys
      $dev_key="DEV-9E4ABEDD687A7893D3E61CDE7009D4900CB0";
      $api_key= "API-02BFF7786901A18D9Y5FAAAD3853435AE646";
  
      curl_setopt($ch, CURLOPT_HTTPHEADER, array("Accept: application/xml", "Authorization: ".$dev_key.":". $api_key));
  
      $result = curl_exec($ch);
      curl_close($ch);
  
      print $result;
  </code></pre>