auto_kid_handling.rb

require 'json/jwt' # v1.6.2+

private_key = OpenSSL::PKey::RSA.generate(2048)

jwk = JSON::JWK.new(private_key)
p jwk[:kid] # => auto-generated kid (= JWK Thumbprint value)

jwt = JSON::JWT.new(
  iss: 'https://idp.example.com',
  aud: 'https://rp.example.com',
  sub: 'user#12345',
  iat: Time.now,
  exp: 5.minutes.from_now
)
p jwt.kid # => nil

jws = jwt.sign(jwk)
p jws.kid # => auto-copied from jwk

jws = jwt.sign(private_key)
p jws.kid # => nil (because OpenSSL::PKey::RSA instance itself doens't have kid)