code: public JWSHeader setX509Certificate(String x509Certificate) {
          this.x509Certificate = x509Certificate;
          this.put(HeaderConstants.X509_CERT, x509Certificate);
          return this;
      }
docs: Sets the X.509 certificate chain header parameter contains the X.509 public key certificate
  or certificate chain corresponding 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>