Thanks quaffapint to raise this point. To be honnest, I hesitated to add this question in the post. Indeed HPACK could partially solve the issue. But as you said, it requires HTTP/2. Btw, HPACK is well explained here: https://developers.google.com/web/fundamentals/performance/h...

I tried in this post to not talk about the "transport". Indeed JWTs can be used with HTTP/1.1, HTTP/2 or even SIP. Furthermore HPACK maybe disabled in some cases. Here is what the RFC 7541 (HPACK) says about Authorization header (https://tools.ietf.org/html/rfc7541#section-7.1.3):

  "An encoder might also choose not to index values for header fields that are considered to be highly valuable or sensitive to recovery, such as the Cookie or Authorization header fields."