code: public JWSHeader setJwk(String jwk) {
          this.jwk = jwk;
          this.put(HeaderConstants.JWK, jwk);
          return this;
      }
docs: Sets the JSON Web Key header parameter that is a public key that corresponds to the key used
  to digitally sign the JWS or {@code null} for none.
  
  <p>
  Overriding is only supported for the purpose of calling the super implementation and changing
  the return type, but nothing else.
  </p>