function defaultState(req, options) {
  const state = { returnTo: options.returnTo || req.originalUrl };
  debug('adding default state %O', state);
  return state;
}
Generate the state value for use during login transactions. It is used to store the intended
return URL after the user authenticates. State is not used to carry unique PRNG values here
because the library utilizes either nonce or PKCE for CSRF protection.

@param {RequestHandler} req
@param {object} options

@return {object}