Editing the payload destroys the header

[nbarbettini]

If I paste the following JWT into the tool:

eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJqdGkiOiIxYjFaMTdLa0xBV09UTUg4cXA2aU1SIiwiaWF0IjoxNDcyNjY0NDU0LCJpc3MiOiJodHRwczovL2FwaS5zdG9ybXBhdGguY29tL3YxL2FwcGxpY2F0aW9ucy83T2wzNzdIVTA2OGxhZ0NZazdVOVhTIiwic3ViIjoiaHR0cHM6Ly9hcGkuc3Rvcm1wYXRoLmNvbS92MS9hY2NvdW50cy80cVRYMlF5UlZoT05kNWVRcDdoVFEwIiwiZXhwIjoxNDcyNjgxNDkwLCJydGkiOiI0NmZBSE90N1laNUVvOFIyMzVQa0YifQ.hLjNfYpf3sQ1rD-Kc9Y0yaEK3TNDq6ohDvEcamM6e7Y

Which as a header like:

{
 "typ": "JWT",
 "alg": "HS256",
 "kid": "4VPVLB6K44RYSKRRVAB4TEBOX",
 "stt": "access"
}

and then edit the payload, the header is rewritten as

{
  "typ": "JWT",
  "alg": "HS256"
}

[bretterer]

Duplicate of #12