New answers tagged database
Oh boy are there! OAuth (Facebook, Google, Twitter), SAML, LDAP, PAM, HTTP Basic, HTTP Client Certificate, IP restriction, 2-Factor authentication, RSA token, biometrics.
Depending on how users access the site, you might be able to authenticate simply by their IP address. There is also HTTP authentication, both basic and digest. But if you need to differentiate between multiple users then these need to be stored somewhere, and regardless of the method used, this is a "database".
You could try using some eternal authentication like OAuth http://oauth.net/ or Facebook Login https://developers.facebook.com/docs/facebook-login/login-flow-for-web/v2.1 I believe OAuth still requires SQL usage though.
Top 50 recent answers are included