addding JWS Header {"alg":"RS256"}
adding JWS Payload for the first time {"iss":"joe", "exp":1300819380, "http://example.com/is_root":true} NOTE: This field will be ignored when this is 2nd time and later since existing payload will be used.
NOTE: You can press 'Append Signature' one or more times to add multiple parallel signatures to a JWS-JS. If you want to change JWS Header and signing key for each signatures, please modify above 'JWS Header' and 'signing key' fields then push 'Append Signature'.