Q:

Active Directory as OpenID provider?

Can an Active Directory be used as a OpenID provider? WIF is an option, but it's quite complicated and not very widespread. 

A:

Yes, you can.  Just host an ASP.NET web site that itself uses Active Directory authentication, and exposes an OpenID Provider using DotNetOpenAuth.  

A:

There is also OpenID-LDAP server which claims to work with AD LDAP.

A:

ADFS 4.0, available from Windows Server 2016 onwards, allows authentication using OpenID. 

