How to use the passport.callback function in passport

}, function(accessToken, refreshToken, profile, done) {
  console.log('Received Facebook profile from: ', profile.displayName);
  return done(null, profile);
});

passport.use(strategy);

passport.serializeUser(function(user, done) {
  done(null, user);
});

passport.deserializeUser(function(user, done) {
  done(null, user);
});

passport.callback = function(req, res, next) {
  passport.authenticate('auth0', function(err, user) {
    if (err) {
      console.log(clc.red('Error: Auth0 ' + err));
      return next(err); // will generate a 500 error
    } else if (!user) {
      console.log('Unknown user logging with FB');
      return res.redirect('/admin?error=1');
    }
    return res.redirect('/admin?user=' + user.displayName);
  })(req, res, next);
}

module.exports = passport;

//     /auth/:provider/callback
    this.authenticate(provider, options)(request, response, request.next);
  }
};

/**
 * Create an authentication callback endpoint
 *
 * For more information on authentication in Passport.js, check out:
 * http://passportjs.org/guide/authenticate/
 *
 * @param {Request}   request
 * @param {Response}  response
 * @param {Function}  next
 */
passport.callback = function callback(request, response, next) {
  sails.log.verbose(__filename + ':' + __line + ' [Service.Passport.callback() called]');

  var provider = request.param('provider', 'local');
  var action = request.param('action');

  if (provider === 'local' && action !== undefined) {
    if (action === 'connect' && request.user) {
      this.protocols.local.connect(request, response, next);
    } else {
      next(new Error('Invalid action'));
    }
  } else {
    // Load authentication strategies
    this.loadStrategies(request);

    // The provider will redirect the user to this URL after approval. Finish

// the provider will redirect the user back to the application at
  //     /auth/:provider/callback
  this.authenticate(provider, options)(req, res, req.next);
};

/**
 * Create an authentication callback endpoint
 *
 * For more information on authentication in Passport.js, check out:
 * http://passportjs.org/guide/authenticate/
 *
 * @param {Object}   req
 * @param {Object}   res
 * @param {Function} next
 */
passport.callback = function (req, res, next) {
  var provider = req.param('provider', 'local')
    , action   = req.param('action');

  // Passport.js wasn't really built for local user registration, but it's nice
  // having it tied into everything else.
  if (provider === 'local' && action !== undefined) {
    if (action === 'register' && !req.user) {
      this.protocols.local.register(req, res, next);
    }
    else if (action === 'connect' && req.user) {
      this.protocols.local.connect(req, res, next);
    }
    else if (action === 'disconnect' && req.user) {
      this.disconnect(req, res, next);
    }
    else {

// the provider will redirect the user back to the application at
  //     /auth/:provider/callback
  this.authenticate(provider, options)(req, res, req.next);
};

/**
 * Create an authentication callback endpoint
 *
 * For more information on authentication in Passport.js, check out:
 * http://passportjs.org/guide/authenticate/
 *
 * @param {Object}   req
 * @param {Object}   res
 * @param {Function} next
 */
passport.callback = function (req, res, next) {
  var provider = req.param('provider', 'local')
    , action   = req.param('action');

  // Passport.js wasn't really built for local user registration, but it's nice
  // having it tied into everything else.
  if (provider === 'local' && action !== undefined) {
    if (action === 'register' && !req.user) {
      this.protocols.local.register(req, res, next);
    }
    else if (action === 'connect' && req.user) {
      this.protocols.local.connect(req, res, next);
    }
    else if (action === 'disconnect' && req.user) {
      this.protocols.local.disconnect(req, res, next);
    }
    else {

// the provider will redirect the user back to the application at
    //     /auth/:provider/callback
    this.authenticate(provider, options)(req, res, req.next);
  };

  /**
   * Create an authentication callback endpoint
   *
   * For more information on authentication in Passport.js, check out:
   * http://passportjs.org/guide/authenticate/
   *
   * @param {Object}   req
   * @param {Object}   res
   * @param {Function} next
   */
  passport.callback = function (req, res, next) {
    var provider = req.param('provider', 'local');
    var action = req.param('action');

    // Passport.js wasn't really built for local user registration, but it's nice
    // having it tied into everything else.
    if (provider === 'local' && action !== undefined) {
      if (action === 'register' && !req.user) {
        this.protocols.local.register(req, res, next);
      } else if (action === 'connect' && req.user) {
        this.protocols.local.connect(req, res, next);
      } else if (action === 'disconnect' && req.user) {
        this.protocols.local.disconnect(req, res, next);
      } else {
        next(new Error('Invalid action'));
      }
    } else {

// the provider will redirect the user back to the application at
  //     /auth/:provider/callback
  this.authenticate(provider, options)(req, res, req.next);
};

/**
 * Create an authentication callback endpoint
 *
 * For more information on authentication in Passport.js, check out:
 * http://passportjs.org/guide/authenticate/
 *
 * @param {Object}   req
 * @param {Object}   res
 * @param {Function} next
 */
passport.callback = function (req, res, next) {
  var provider = req.param('provider', 'local')
    , action   = req.param('action');

  // Passport.js wasn't really built for local user registration, but it's nice
  // having it tied into everything else.
  if (provider === 'local' && action !== undefined) {
    if (action === 'register' && !req.user) {
      this.protocols.local.register(req, res, next);
    }
    else if (action === 'connect' && req.user) {
      this.protocols.local.connect(req, res, next);
    }
    else if (action === 'disconnect' && req.user) {
      this.disconnect(req, res, next);
    }
    else {

//     /auth/:provider/callback
        this.authenticate(provider, options)(request, response, request.next);
    }
};

/**
 * Create an authentication callback endpoint
 *
 * For more information on authentication in Passport.js, check out:
 * http://passportjs.org/guide/authenticate/
 *
 * @param   {Object}    request
 * @param   {Object}    response
 * @param   {Function}  next
 */
passport.callback = function(request, response, next) {
    var provider = request.param('provider', 'local');
    var action = request.param('action');

    if (provider === 'local' && action !== undefined) {
        if (action === 'connect' && request.user) {
            this.protocols.local.connect(request, response, next);
        } else {
            next(new Error('Invalid action'));
        }
    } else {
        // Load authentication strategies
        this.loadStrategies(request);

        // The provider will redirect the user to this URL after approval. Finish
        // the authentication process by attempting to obtain an access token. If
        // access was granted, the user will be logged in. Otherwise, authentication

// the provider will redirect the user back to the application at
  //     /auth/:provider/callback
  this.authenticate(provider, options)(req, res, req.next);
};

/**
 * Create an authentication callback endpoint
 *
 * For more information on authentication in Passport.js, check out:
 * http://passportjs.org/guide/authenticate/
 *
 * @param {Object}   req
 * @param {Object}   res
 * @param {Function} next
 */
passport.callback = function (req, res, next) {
  var provider = req.param('provider', 'local')
    , action   = req.param('action');

  // Passport.js wasn't really built for local user registration, but it's nice
  // having it tied into everything else.
  if (provider === 'local' && action !== undefined) {
    if (action === 'register' && !req.user) {
      this.protocols.local.register(req, res, next);
    }
    else if (action === 'connect' && req.user) {
      this.protocols.local.connect(req, res, next);
    }
    else {
      next(new Error('Invalid action'));
    }
  } else {

// the provider will redirect the user back to the application at
  //     /auth/:provider/callback
  this.authenticate(provider, options)(req, res, req.next);
};

/**
 * Create an authentication callback endpoint
 *
 * For more information on authentication in Passport.js, check out:
 * http://passportjs.org/guide/authenticate/
 *
 * @param {Object}   req
 * @param {Object}   res
 * @param {Function} next
 */
passport.callback = function (req, res, next) {
  var provider = req.param('provider', 'local')
    , action   = req.param('action');

  // Passport.js wasn't really built for local user registration, but it's nice
  // having it tied into everything else.
  if (provider === 'local' && action !== undefined) {
    if (action === 'register' && !req.user) {
      this.protocols.local.register(req, res, next);
    }
    else if (action === 'connect' && req.user) {
      this.protocols.local.connect(req, res, next);
    }
    else if (action === 'disconnect' && req.user) {
      this.protocols.local.disconnect(req, res, next);
    }
    else {

// the provider will redirect the user back to the application at
  //     /auth/:provider/callback
  this.authenticate(provider, options)(req, res, req.next);
};

/**
 * Create an authentication callback endpoint
 *
 * For more information on authentication in Passport.js, check out:
 * http://passportjs.org/guide/authenticate/
 *
 * @param {Object}   req
 * @param {Object}   res
 * @param {Function} next
 */
passport.callback = function (req, res, next) {
  const provider = req.param('provider', 'local'),
    action   = req.param('action');

  // Passport.js wasn't really built for local user registration, but it's nice
  // having it tied into everything else.
  if (provider === 'local' && action !== undefined) {
    if (action === 'register' && !req.user) {
      this.protocols.local.register(req, res, next);
    } else if (action === 'connect' && req.user) {
      this.protocols.local.connect(req, res, next);
    } else if (action === 'disconnect' && req.user) {
      this.disconnect(req, res, next);
    } else {
      next(new Error('Invalid action'));
    }
  } else {