Authenticators is now a map of keys -> service names. The key is used
in things such as URL segments. The “default_authenticator” value has
been replaced with the key “default” in this map, although in time a
default authenticator may not be needed.
IX: Refactor login() to avoid code duplication on single/multiple handlers
IX: Refactor LoginHandler to be more amenable to extension
IX: Fixed permissionFailure hack
his LoginHandler is expected to be the starting point for other
custom authenticators so it should be easier to repurpose components
`of it.
IX: Fix database-is-ready checks in tests.
IX: Fixed MemberAuthenticatorTest to match the new API
IX: Update security URLs in MemberTest
