code: function promptToAuthorize (req, res, next) {
    var params = req.connectParams
    var client = req.client
    var user = req.user
    var scopes = req.scopes
  
    // The client is not trusted and the user has yet to decide on consent
    if (client.trusted !== true && typeof params.authorize === 'undefined') {
      // check for pre-existing consent
      AccessToken.exists(user._id, client._id, function (err, exists) {
        if (err) { return next(err) }
  
        // if there's an existin authorization,
        // reuse it and continue
        if (exists) {
          params.authorize = 'true'
          next()
  
        // otherwise, prompt for consent
        } else {
          // render the consent view
          if (req.path === '/authorize') {
            res.render('authorize', {
              request: params,
              client: client,
              user: user,
              scopes: scopes
            })
  
          // redirect to the authorize endpoint
          } else {
            res.redirect('/authorize?' + qs.stringify(params))
          }
        }
      })
  
    // The client is trusted and consent is implied.
    } else if (client.trusted === true) {
      params.authorize = 'true'
      next()
  
    // The client is not trusted and consent is decided
    } else {
      next()
    }
  }
docs: Prompt to authorize