We've rolled our own (zero frills) so far, but are looking at PropelAuth (https://www.propelauth.com/) to add MFA and other bells and whistles and we like what we see. (Full disclosure, they've become friends of ours through YC)
Thanks! I’m the founder of PropelAuth - our focus is providing user authentication for b2b businesses. We did a launch HN[0] a while back if you want to read more about us.
