[Twisted-Python] Must avatarId always be a string?

[Peter Westlake]

http://twistedmatrix.com/documents/current/core/howto/cred.html says
that the avatarId parameter to IRealm.requestAvatar must be a string,
not even a Unicode string. I'm using LDAP for authentication, and the
checker retrieves the full LDAP entry for the user as a side-effect of
authentication. Until I read that doc I was happily passing back the
tuple of LDAP details as an avatarId, and it all works perfectly well.
Is it really wrong, and if so, how will it fail? And what should I do
instead to pass back the details?

Peter.