function complete() {
            if (options.successReturnToOrRedirect) {
              var url = options.successReturnToOrRedirect;
              if (req.session && req.session.returnTo) {
                url = req.session.returnTo;
                delete req.session.returnTo;
              }
              return res.redirect(url);
            }
            if (options.successRedirect) {
              return res.redirect(options.successRedirect);
            }
            next();
          }
Authenticate `user`, with optional `info`.

Strategies should call this function to successfully authenticate a
user.  `user` should be an object supplied by the application after it
has been given an opportunity to verify credentials.  `info` is an
optional argument containing additional user information.  This is
useful for third-party authentication strategies to pass profile
details.

@param {Object} user
@param {Object} info
@api public