Doorkeeper is an OAuth 2 provider for Ruby on Rails / Grape
Doorkeeper is a gem (Rails engine) that makes it easy to introduce OAuth 2 provider functionality to your Ruby on Rails or Grape application. Doorkeeper is an oAuth2 provider built in Ruby. It integrates with Ruby on Rails and Grape frameworks. The installation process depends on the framework you're using. Doorkeeper follows Rails maintenance policy and supports only supported versions of the framework.
PHP strong authentication library, web interface & CLI, OATH certified
...The data storage of the command line utility is by default flat files based in order to simplify deployment in a few minutes, but MySQL backend is supported too.
multiOTP can be easily integrated in RADIUS servers like FreeRADIUS under Linux/Windows or TekRADIUS LT under Windows.
multiOTP is also the engine of the credential provider multiOTP Credential Provider.