User system refactor

[lunny]

Current Status

• On the user table, there are two columns LoginType and LoginSource which will decide how to authenticate the user, so a user's login type could be one of NoType , Plain, LDAP, SMTP, PAM, DLDAP, OAuth2, SSPI

When login, first get the database record according to user's input login name on user table. If the record exist, then check user's login type. If login type supports password check, just check password from source.
If the user doesn't exist, then check all possible login sources one by one with give login name and password.

The input username and password will be checked. For some login sources, if password is right but users doesn't exist in database then create one user.

TBC