Firebase Authentication with multi-factor authentication

Firebase Authentication with multi-factor authentication should soon be available according to this Google I/O video

Update: June 2020

From March 12, 2020, It is now possible to set up multi-factor authentication using SMS as 2nd factor with Firebase for Google Cloud Identity Platform projects but this is a paid service. This article shows you how to add SMS multi-factor authentication to your web app.

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I am quoting from github firebase repo. here.

Firebase Auth does not support multi-factor authentication. FirebaseUI cannot support this feature until the underlying SDK supports it. For 2-factor auth, 2 credentials need to be passed to get a Firebase ID token. Currently, one is enough to get an ID token. You can submit an official request for multi-factor auth with Firebase support.

However Multi-factor authentication itself works fine with Google account and FirebaseUI if it is enabled from Google settings.

hope it helps.