I'm using OpenID much the same as here on StackOverflow to authenticate my users. What I really need to be able to do though is have that OpenID work across all sub-domains of my site.

The site behaves much the same as Kijiji in that each region has it's own subdomain

• calgary.example.com
• toronto.example.com
• vancouver.example.com
• etc

When a user logs into "calgary" and later logs into "toronto", they will be forced to "give permission" at the provider, thus resulting in a new OpenID and resulting also in a new login.

My app "can" have multiple OpenID's under one account, but that would become cumbersome to manage.

Is there a way to have the provider link up to the top level domain and subsequently work across all sub-domains?

I'm using DotNetOpenAuth.