reduce duplication and remove dependency to base64

[deepu105]

Summary

I took some inspiration from this project for https://github.com/jwt-rs/jwt-ui, I made some improvements. So contributing that back if there is interest.

• Support JWKS secret for all supported algorithms
• Reduce duplication
• Remove unwanted base64 dependency
• Move utils to seperate file

Preflight checklist

• [x] Code formatted rustfmt ($ cargo fmt)
• [x] Code linter check with clippy ($ cargo clippy)
• [x] Relevant tests added
• [x] Any new documentation added

[mike-engel]

@deepu105 sorry for the silence on this. Can you rebase/update your branch with main?

[deepu105]

done