/**
  * Gets the HTTP headers for the report download request.
  * @param AdWordsUser $user the AdWordsUser to get credentials from
  * @param string $url the URL the request will be made to
  * @param array $options the options for the download
  * @return array and array of strings, which are header names and values
  */
 private static function GetHeaders($user, $url, array $options = NULL)
 {
     $headers = array();
     $version = !empty($options['version']) ? $options['version'] : $user->GetDefaultVersion();
     // Authorization.
     if ($user->GetOAuthInfo()) {
         $oauthParams = $user->GetOAuthHandler()->GetSignedRequestParameters($user->GetOAuthInfo(), $url, 'POST');
         $headers['Authorization'] = 'OAuth ' . $user->GetOAuthHandler()->FormatParametersForHeader($oauthParams);
     } elseif ($user->GetOAuth2Info()) {
         if (!$user->IsOAuth2AccessTokenValid() && $user->CanRefreshOAuth2AccessToken()) {
             $user->RefreshOAuth2AccessToken();
         }
         $oauth2Header = $user->GetOAuth2Handler()->FormatCredentialsForHeader($user->GetOAuth2Info());
         $headers['Authorization'] = $oauth2Header;
     } else {
         $headers['Authorization'] = 'GoogleLogin auth=' . $user->GetAuthToken();
     }
     // Developer token.
     $headers['developerToken'] = $user->GetDeveloperToken();
     // Target client.
     $email = $user->GetEmail();
     $clientId = $user->GetClientId();
     if (isset($clientId)) {
         if (strpos($clientId, '@') !== FALSE) {
             if ($version < 'v201109') {
                 $headers['clientEmail'] = $clientId;
             } else {
                 throw new ReportDownloadException('Client emails are not supported ' . 'in versions v201109 and later.');
             }
         } else {
             $headers['clientCustomerId'] = $clientId;
         }
     } else {
         if ($version < 'v201109' && isset($email)) {
             $headers['clientEmail'] = $email;
         } else {
             throw new ReportDownloadException('The client customer ID must be ' . 'specified for report downloads.');
         }
     }
     // Flags.
     if (isset($options['returnMoneyInMicros'])) {
         $headers['returnMoneyInMicros'] = $options['returnMoneyInMicros'] ? 'true' : 'false';
     }
     return $headers;
 }