asterisk users - Jan 2006 - Question on SIP Domains and registration

Hello,

I have a situation where I need to differentiate between registrations 
by users where there might be clashes on the left hand side (username) 
portion of the SIP From URI. (for a multi-domain virtual hosting system)

It seems that only the username portion is used for SIP authentication, 
and this means that I have clashes.

I need to find a way that asterisk can differentiate between 
user@domain1.com and user@domain2.com

Does anyone have any idea? Asterisk is being used as the PSTN gateway, 
where all registrations take place on OpenSER.

Thanks.

-- 

-Barry Flanagan