Support getting of JWKS from local file system for JWT verification purposes

[dadrus]

Preflight checklist

• I agree to follow this project's Code of Conduct.
• I have read and am following this repository's Contribution Guidelines."
• I have discussed this feature request with the community.

Describe the background of your feature request

Some systems use symmetric keys to sign JWTs. Even symmetric keys can be used by heimdall to verify the corresponding mac, the only currently supported way to get such keys is via an JWKS endpoint. Obviously, exposing symmetric keys via an endpoint is a bad idea.

Describe your idea

Allow heimdall to fetch JWK documents not only from endpoints, but also from the local file system.

Are there any workarounds or alternatives?

No

Version

v0.7.0-alpha

Additional Context

No response