Comment 6 for bug 397610

We might have issues with unicode usernames, I have fixed two such bugs (Bug #495872 and http://bazaar.launchpad.net/~schooltool-owners/schooltool.gradebook/trunk/revision/163).

But this error, that prevents such users from loggin in, is a bug #131460 in zope.publisher that will be fixed in 3.12.4 (unreleased). When that is released, use it in development schooltool, remove the usernames restriction, and look for more bugs.

Douglas' comment #3 suggests storing an encoded principal id. The fix in zope.publisher is similar, except that it uses principal.id.encode('ascii', 'backslashreplace') instead of id.encode("punycode") and does that only for log messages, id is stored as unicode.