indielogin.com

 indielogin.com  is a service that developers can use to log users in to a website.

The developer creates a web sign-in form that asks for the user's domain, and it directs people to indielogin.com to authenticate. Users can authenticate by linking to one or more existing authentication providers such as Twitter, GitHub, or the user's own IndieAuth server.

Demo
You can try out a demo by logging into the sample app at https://pin13.net/login/

Documentation

 * https://indielogin.com/setup
 * How to set up your domain to log in via indielogin.com
 * https://indielogin.com/api
 * Developer documentation for using indielogin.com to authenticate users

Examples

 * This IndieWeb wiki uses indielogin.com to authenticate users and then allows them to edit it. See How to Join the IndieWeb Wiki