lib/oauth.js
function passportCallback(provider, options, operation) {
    return function(req, res, next) {
      var theOptions = extend({}, options);
      if(provider === 'linkedin') {
        theOptions.state = true;
      }
      var accessToken = req.query.bearer_token || req.query.state;
      if(accessToken && (stateRequired.indexOf(provider) > -1 || config.getItem('providers.' + provider + '.stateRequired') === true)) {
        theOptions.state = accessToken;
      }
      theOptions.callbackURL = getLinkCallbackURLs(provider, req, operation, accessToken);
      theOptions.session = false;
      passport.authenticate(provider, theOptions)(req, res, next);
    };
  }
function passportCallback(provider, options, operation) {
    return function(req, res, next) {
      var theOptions = extend({}, options);
      if(provider === 'linkedin') {
        theOptions.state = true;
      }
      var accessToken = req.query.bearer_token || req.query.state;
      if(accessToken && (stateRequired.indexOf(provider) > -1 || config.getItem('providers.' + provider + '.stateRequired') === true)) {
        theOptions.state = accessToken;
      }
      theOptions.callbackURL = getLinkCallbackURLs(provider, req, operation, accessToken);
      theOptions.session = false;
      passport.authenticate(provider, theOptions)(req, res, next);
    };
  }
Configures the passport.authenticate for the given provider, passing in options Operation is 'login' or 'link'