www.hbogo.com
Click on "Sign In" and select your provider.
Click on Verizon FIOS
You see a popup from verizon show up to allow you to enter your Verizon username and password.
https://www.kickstarter.com/login Click on "Login with Facebook"
and there are tons of more examples.
Notice in the above examples you see a popup served from the authenticating domain (in the first case you see a Verizon popup and in the second case you see a Facebook popup). Clearly Verizon FIOS and Facebook have written code (a web service?) that allows client websites (like HBOGO.com and Kickstarter.com) to easily authenticate.
I want to create a web service similar to what Verison FIOS or Facebook and I was wondering if there is any sample code I could follow that would help me get started? The goal would be to have other clients authenticate with my webservice (just like HBOGO and KickStarter authenticate through Verizon FIOS and Facebook respectively).