How to solve problem: 'xEntities': type used in a using statement must be implicitly convertible to 'System.IDisposable' when use using block to open Entity Framework data context?

Need to add EntityFramework.dll reference into your project file.

What is Open ID and its workflow?

OpenID allows you to use an existing account to sign in to multiple websites, without needing to create new passwords.
From:  http://openid.net/get-an-openid/what-is-openid/

OpenID 2.0 interaction sequence from Google
https://developers.google.com/accounts/docs/OpenID?csw=1#Interaction