Custom MySQL Auth + Password = SHA512 + User Autocreate

[littlet]

I need to integrate 'MantisBT 1.2.19' to another system in the web. The following should work:
- The users login via IMAP auth to the MantisBT system, 'username' and 'password' locate other database, not in MantisBT.
- If the user is logged in the MantisBT and not exists the user, the MantisBT is autocreate it to the first login.
- The format of the password should be SHA512.

Thank's all helps!