Allow setting sensitive configuration values to be read from files

[thcrt]

See title. Would be helpful for integration with Secrets.

For example:

[auth.fetch]
token.literal = "qwertyuiop1234567890"

[auth.fetch]
token.file = "/run/secrets/auth_token"

[4censord]

While you are on this, might i suggest also allowing them to be read from env vars?
that would allow easy integration with kubernetes secrets

[thcrt]

While you are on this, might i suggest also allowing them to be read from env vars? that would allow easy integration with kubernetes secrets

Sounds like a good idea. Env vars are very helpful, it's just annoying to deal with them given their somewhat unstructured nature. When this gets implemented, I'd probably recommend (but not enforce) that this is only done in a containerised/virtualised environment where setup is reproducible & immutable.

[thcrt]

@4censord I'm planning to start using tattl for configuration, so this could be a feature that I implement there.