Special characters in ssh usernames

I've got a few users configured on LDAP, and would like them to be able to connect to a Linux machine via SSH using those users and password on the LDAP directory.
However, there are 2 issues I do not know how to handle:

1. The usernames and passwords are in unicode. Is this a problem for OpenSSH?
2. Some usernames are of the form "user@something". Is it possible to leave those "@" signs in? So that a user will be able to perform ssh user@something@computer ?

Thanks!

The user names are just bytes. So if all machines use UTF-8, then there shouldn't be a problem. The passwords should work similarly, but the details would depend on what is actually verifying the passwords on the remote end (e.g., PAM), which could mess it up.

It's best to try it out with your exact setup, of course. But it should work.