This error occurs when our users "Block third-party cookies and site data".
To replicate the error, go to:
We always advise our users to Uncheck the blocking of third-party cookies and site data; however, some users still prefer to block it.
One can still sign in to their Gmail with this blocked. Interestingly, why can't our users sign in using the Firebase-Google OAuth provided with their third party cookies & site data blocked?
We are built with Angular2 and Firebase. Is there no way that the users can still authenticate with third-party cookies and site data blocked?
The domain you're using is deeptent.com, but the domain that firebase is authenticating against and setting cookies from is your .firebaseapp.com domain. So, yes, the cookies are considered third-party. The firebase folks really should take a harder look at how they are connecting custom domains in the firebase hosting setup. Also, see here: Use Google Firebase Authentication without 3rd Party Cookies