code: def get_token(self, user_id, password, redirect_uri,
                    scope='/read-limited'):
          
          response = self._authenticate(user_id, password, redirect_uri,
                                        scope)
          return response['access_token']
docs: Get the token.
  
          Parameters
          ----------
          :param user_id: string
              The id of the user used for authentication.
          :param password: string
              The user password.
          :param redirect_uri: string
              The redirect uri of the institution.
          :param scope: string
              The desired scope. For example '/activities/update',
              '/read-limited', etc.
  
          Returns
          -------
          :returns: string
              The token.