code: function getDigest(req) {
      // most other servers
      var digest = req.headers["authorization"];
      if (digest && digest.toLowerCase().indexOf("digest") === 0)
          return digest.substr(7);
      else
          return null;
  }
docs: This method returns the full digest string.
  
  If the header could not be found, null will be returned
  
  @return mixed