code: function unstashParams (req, res, next) {
    // OAuth 2.0 callbacks should have a state param
    // OAuth 1.0 must use the session to store the state value
    var id = req.query.state || req.session.state
    var key = 'authorization:' + id
  
    if (!id) { // && request is OAuth 2.0
      return next(new MissingStateError())
    }
  
    client.get(key, function (err, params) {
      if (err) { return next(err) }
  
      // This handles expired and mismatching state params
      if (!params) { return next(new ExpiredAuthorizationRequestError()) }
  
      try {
        req.connectParams = JSON.parse(params)
      } catch (err) {
        next(err)
      }
  
      next()
    })
  }
docs: Unstash authorization params