public static function createClient($clientName = CoreConstants::CLIENT_CURL){
      if($clientName == CoreConstants::CLIENT_CURL){
         if(extension_loaded('curl')){
            return new CurlHttpClient();
         }else{
            throw new SdkException("curl extension is not enabled. Cannot create curl http client for the SDK.");
         }
      }

      if(strcasecmp($clientName, CoreConstants::CLIENT_GUZZLE) == 0 ||strcasecmp($clientName, CoreConstants::CLIENT_GUZZLE_FULL) == 0){
          if(class_exists('GuzzleHttp\Client')){
             return new GuzzleHttpClient();
          }else{
            throw new SdkException("guzzle client cannot be found. Cannot create guzzle http client for the SDK.");
          }
      }

      throw new SdkException("The client Name you passed is not supported. Please use either 'curl' or 'guzzle' for the client Name.");
  }