GTM: override oauth referrals

custom variable.js

/* 
  Based on: 
  - https://www.simoahava.com/gtm-tips/implement-referral-exclusions-via-gtm/ 
  - https://medium.com/@postman31/dont-let-oauth-fools-your-analytics-88d56523f6b1
  - https://www.thyngster.com/tip-maintaining-proper-session-attribution-in-ga-when-using-oauth-providers-with-google-tag-manager/
*/

function() {
  /* When the user goes thru oauth, the referrer is FB so the session is restarted
     See: https://medium.com/@postman31/dont-let-oauth-fools-your-analytics-88d56523f6b1
  */
  var authProviders = [
    // Matches FB oauth:
    // https://www.facebook.com/dialog/oauth
    // https://www.facebook.com/v3.3/dialog/oauth?
    // https://www.facebook.com/v2.4/dialog/oauth
    /www\.facebook\.com\/(.+)\/oauth\b/,
  ];
  var referrer = {{Referrer}};
  if (referrer) { 
    for (var i = authProviders.length-1; i >= 0; i--) {
      if (new RegExp(authProviders[i]).test(referrer)) {
        // Set referrer to current location, so this referrer is not counted
        return null;
      }
    }
  }
  return referrer;
}