I have a situation where I want users to have the same signon (same user record in the database) on 2 different DNN portals that have completely different domains, but are hosted on the same installation. Is this possible out of the box with DNN? Looks like there are some 3rd party tools for this but I don't want to resort to that if at all possible.
Looking at the dnn schema, there is a table called UserPortals that appears to relate one userid(account) to multiple portals (portalID) as the composite,primary key.

Thanks

This isn't supported out of the box.

I have used DNN Masters' MPUS-X module with good results. I have had one problem related to Profile Pictures across websites, but that is all. Apparently, the profile pictures is implemented differently from other profile properties in DotNetNuke. I haven't check recently, so maybe they have figured out a way to deal with the problem.

If you google for "DotNetNuke single signon" you will find additional information.

Data Springs' Dynamic Login supports single signon:

"New Single Sign On (SSO) functionality. This new enhancement allows for other portals within the DNN installation to be able to access the portal if the SSO feature is turned on and the user enters the login credentials correctly for the 'Master Portal'. Additionally there is an optional 'Reverse SSO' feature to automatically add the user to the master portal if they are signing into the portal and that user doesn't exist within the master portal. "