On Thu, Dec 10, 2020 at 6:32 PM Vinnie Falco via Boost-users <boost-users@lists.boost.org> wrote:
You can copy the code into your own source file and edit to suit your needs

FWIW, according to https://tools.ietf.org/html/rfc7515#appendix-C,
I can easily wrap Beast's encoder/decoder to yield JWT-required base64url encoding.
The decoder I referenced wouldn't know about - an _ chars used in that variant anyway.