Gracefully return user to login page and notify about an login error

[KnickKnack]

Hi all,

still continuing on my OAuth2 plugin implementation, I've a problem I can't actually solve and need you valuable advises.

I've this fragment in my plugin

OAuth.getStrategy = function (strategies, callback) {
  winston.verbose('[maxonID] --> OAuth.getStrategy');
  if (configOk) {
    passportOAuth = require('passport-oauth2');

    passportOAuth.Strategy.prototype.userProfile = function (accessToken, done) {
      if (!accessToken) {
        done(new Error('Missing token, cannot call the userinfo endpoint without it.'));
      }
      this._oauth2.useAuthorizationHeaderforGET(true);
      this._oauth2.get(constants.userRoute, accessToken, function (err, body, res) {
        if (err) {
          console.error(err);
          return done(new Error('Failed to get user info. Exception was previously logged.'));
        }

        if (res.statusCode < 200 || res.statusCode > 299) {
          return done(new Error('Unexpected response from userInfo. [' + res.statusCode + '] [' + body + ']'));
        }

        OAuth.validateEntitlement(accessToken, constants.allowedEntitlement, function (err, accessAllowed) {
          if (err) {
            return done(err);
          }

          if (!accessAllowed) {
            // Need to find a way to gracefully notify the user and point back to login page
            return done(new Error('Forum access is not granted. Please contact your representative.'));
          }

          try {
            var json = JSON.parse(body);
            OAuth.parseUserReturn(json, function (err, profile) {
...

and I'd like to return the user to the forum login page and notify him about the issue, something like when the password is wrong. Is there a smart way to make it happen from such a plugin without rising an error?

Thanks a lot for your valuable insights, R.