I actually just finished integrating Clef (
https://getclef.com/) into one of my sites (
https://CoinDaddy.io) to handle 2-factor authentications and it works great!
Previously I was using gauthify.com and paying like $25/mo for the service. The Clef service is 100% free for companies to use for login authentication... I think you only pay if you want some premium features. Also the fact that your able to register on a site, or login to a site simply by scanning the screen with your phone is way faster than typing out registration/login details. Not to mention the wave login page looks wicked cool... no more boring qrcodes or typing google authenticator codes.
The staff was also really friendly. I signed up as a developer and within a few minutes I had an email from a company staff member offering help with the integration, which only took a few minutes. They helped test the integration and have been nothing but highly professional.
If anyone is looking for some good/cheap/secure 2FA authentication for their website, I would highly suggest getclef.com
And no... this is not a paid shill account.. I just created this account a few minutes ago because I don't use this forum very often and can't remember the password to my old account.
J-Dog