Carry login across servers

Currently, eterna rests within:
stanford.edu
cmu.edu
eternagame.org

plus various other paraphenalia:
eternawiki.org
getsatisfaction.com

Now, during the normal browsing of the game, the site sometimes jumps me in between the first three, and then I am anonymous again.
Would it be possible to make a login that holds across all the domains? Or would that be a hackable security problem?

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