How do sites like stackoverrflow using the third party login id, to login to the site?

How the sit开发者_高级运维es like stackoverrflow using the third parthy login id(gmail,blogspot), to login the site?

How to do this in asp.net? Give me a idea to implement this in to my application.

i don't have idea from where. I have to start this.

OpenID is a decentralized system for authenticating users via third-party OpenID providers, Google and AOL among them.

http://openid.net/

http://en.wikipedia.org/wiki/OpenID

http://weblogs.asp.net/plip/archive/2008/02/02/openid-in-asp-net.aspx

Its called OpenID, something specifically for asp.net you'll find here

It's OPEN ID. You have a .NET client here. This client will allow you to create open id-enabled applications more easily.

From Wikipedia

OpenID is an open, decentralized standard for authenticating users that can be used for access control, allowing users to log on to different services with the same digital identity where these services trust the authentication body. OpenID replaces the common log on process that uses a login-name and a password, by allowing a user to log in once and gain access to the resources of multiple software systems. The term OpenID can also refer to an ID used in the standard.