Separate keys for every client

[solaluset]

Feature Proposed Hello. First of all, thanks for developing this project - it is quite cool and simple.

As for now, only one client public key can be configured, which means that all clients must share the private key. This design is not very secure. I suggest adding support for multiple keys.

Use Case Sharing private keys between several clients is generally not a good idea - there is no way to distinguish them, and if it leaks, the entire system will be compromised. I also want to have the ability to revoke one client without disrupting others.