Implement the core JWT functionality

[dk1844]

Implement the core JWT functionality

• use public key signatures - a public/private key needs to be created. Private key is to be referenced in cofiguration (part of #5).
• an endpoint should exists to interface with the Logee.
• for the first implementation, a simple in memory/config-based user credentials can be used. Hint: look at Enceladus' in-memory implementation