Add Support for JWT Files

[danagarcia]

Adds support for JWT files as per it's RFC, cited below.

Citations:
RFC7519: https://datatracker.ietf.org/doc/html/rfc7519#section-10.3.1

[abonander]

There's no file extension explicitly registered there. Is .jwt something that's starting to appear in practice?

[danagarcia]

In instances where JSON Web Tokens have to be stored as a file it was preferred to use either .txt or .jwt. I don't think there is a standard in the RFC for it; however, .txt is very broad and doesn't allow for easily identifying the file by extension.

If it has to be in the RFC which I would understand given we have to hold some standard, then maybe this is a case where the PR would be rejected on that grounds. I understand either way.

[abonander]

This isn't meant to be a prescriptive source. It isn't really the place to propose a new file extension. Even mime-db, which aggregates several sources, doesn't recognize any file extensions for JWTs: https://github.com/jshttp/mime-db/blob/80b4e6ee439509e9fac9ca3c6befd159519e7ccc/src/apache-types.json#L204

So I'm torn. It's the obvious choice for a file extension, sure, and file extensions have historically been assigned ad hoc anyway, but I've never seen an application store a plaintext JWT on-disk without any other context. It's usually in some sort of config file.

If you can cite any specific applications that do this and why, then sure. Otherwise, it doesn't really make sense to add here.