I wrote a scala JWT library on a weekend when I was more of an intermediate developer (6 years ago?) and it started to be used. But I never ran it in production and flaws were found in it. As a consultant 5 years later I found a customer using it and told them to use someone else's :).

I'm not a security expert - one of the strengths is one of the weaknesses - that's it's a simple spec to implement so your average Joe can implement it, but imperfectly.