How to verify users group membership from VB cookie

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Hi All,

I need to integrate the vb user/group system into a secondary php system.

The script should return the username if:

1. The users vb cookie is in a logged in state (dont know if it can exist and not be in a logged-in state).

2. The user is a member of a special group. (Hardcoded groupname)

Otherwise the script should return a blank and the receiving system will tell the visitor to log into VB first and/or join the appropiate group .

Oh, and the script should work across domains!, i.e. I need to return the user name or the blank to www.site1.com from www.site2.com.

Any ideas to the various levels in the above?

/Tim