c# - Session state are different for same domain with/without www prefix -

i have azure(c#/mvc) project uses session state. store sessions in cache shared in memory of role instances. session state stored in http://mydomain.com , http://www.mydomain.com different. how fix this?

even though question not tagged, assume using iis hosting mvc project on azure , using cookies session management.

in case need consolidate domains 1 in web.config:

<httpcookies domain="mydomain.com"/> 

now both subdomain , main domain should have same session ids.