Auth systems/AuthStack

Data flow
Flows for login and signup.



Open Issues

 * User or ExternalUser as input to autocreate process
 * Does each Authn provider get to autocreate? How will an authn provider disable it, e.g., ldap
 * Is "more info" in Authn a generic additional step? Or does each provider handle it
 * Doe we have a "more info" on account creation?
 * Passwords should be moved to a library, so basic and centralauth providers (or externaluser's for them) can use the same Password formats