Desktop mode has no use for the kerberos, ldap, mfa, oauth2 or webserver
authentication providers: AUTHENTICATION_SOURCES defaults to internal, MFA is
inert because mfa_enabled() requires SERVER_MODE, and get_logout_url() already
guards its kerberos and oauth2 branches on SERVER_MODE. So skip importing and
initialising them unless SERVER_MODE is set, leaving desktop mode with
internal authentication alone.
The accompanying test needed wiring into our own runner before it would ever
execute: web/pgadmin/authenticate/tests/ had no __init__.py, so pkgutil did
not report it and find_modules() never reached the module, and the test class
derived from unittest.TestCase rather than BaseTestGenerator, so the
TestsGeneratorRegistry metaclass never registered it and get_suite() could not
pick it up. Both are fixed here, and the two scenarios now run and pass under
regression/runtests.py.
The test no longer asserts that pgadmin.authenticate.mfa is absent from
sys.modules in desktop mode, because it is not: both pgadmin/browser/__init__
and pgadmin/user_login_check import pgadmin.authenticate.mfa.utils
unconditionally. The original assertion only held because the test itself
popped the module first.
