Pluggable authentication system

[robvdl]

Just creating this ticket for later.

Please remember this project is an experimental project, putting the credentials in the Redis session is OK for learning.

But at some point if corporations ever decide to use this, the putting of credentials in the Redis session may not be suitable for their environment.

In which case we need to discuss how to handle this going forward in some sort of pluggable way.

For now, the only backend will continue being Redis.