STS Authentication and Registration

Hi,

I have a scenario in our project for authenticating and registering users by external service. To be specific there will be a middleware that is connected to user store. The middleware will expose API to login and register new users. I know I can develop some custom widgets for them and have my own API calls to do that. Is there any way I use STS (if it's required) and built in Sitefinity security provider for this?

Note : No user information will be stored inside sitefinity. This requirement only for front end site visitors. Admin users can be registered with in Sitefinity.