feat: Reading username and password from a file

[kugland]

It would be nice to have the possibility of reading username and password from a file. That would help me with secret management on my Nix configuration, so I don’t have to store the password as plain-text in the config.

[kugland]

This would solve it: #147

[micielski]

Wouldn't writing a home manager module for rustmission be a better choice here?

[kugland]

Yes, that would be possible. The solution I have in my Home Manager config is to have a rustmission config stored in plaintext in the /nix/store, and patching it on the activation script to include the secrets from agenix (the secret management system I use).