code: function () {
      // Get stored auth data.
      var stored = this.storage.get();
  
      // If nothing stored, proceed with new authorization
      if (!stored) {
        this.log('No auth data stored, starting authorization from scratch...');
        return this.auth.authorize();
      }
  
      // Otherwise, set the auth data on the Request object so that it can be used for requests
      this.log('Auth data stored, checking validity...');
      this._auth = utils.unserialize(stored);
  
      // Use the saved auth data to check if we're already authorized. If not, it will clear the stored
      // data, then proceed with new authorization.
      return this.auth.isAuth()
        .then(function(result) {
          if (result === false)
            return this.auth.authorize();
        }.bind(this));
    }
docs: Call this method in order to authenticate with SAFE, using either previous authentication
  or new.
  @returns {Promise}