Enhancements on secret handling

[smancke]

Some ideas:

• The generated secret could be stored in a file, to be preserved through reboots.
• Support for asymmetric encryption would be good. In that case, the public key could be provided via rest resource.
• For key rotation in production, a list of keys should be supported in caddy-jwt and loginsrv
• Auto key rotation would be cool

[jeslinmx]

+1 for both point 1 and 3. Additionally, the ability to specify the path to a private key stored in a .pem in jwt-secret would be nice too (and probably a pre-requisite for point 1).