Ok, here's more :) Thanks for your help!
db.define_table('auth_account',
Field('subdomain','string',length=255,required=True),
...
)
db.define_table('auth_many', #many to many relationship
Field('account_id','reference
auth_account',default=db.auth_account.id,required=True),
Field('user_id','reference
auth_user',default=auth.user_id,required=True)
)
if auth.is_logged_in():
>> myset = db(
>> (db.auth_account.id==db.auth_many.account_id) &
>> (db.auth_many.user_id==auth.user_id)
>> )
>> session.account = myset.select(db.auth_account.ALL).first()
