code: public boolean hasPrivateKey() {
  
          if (JsonWebKeyType.OCT.equals(kty)) {
              return k != null;
          } else if (JsonWebKeyType.RSA.equals(kty) || JsonWebKeyType.RSA_HSM.equals(kty)) {
              return (d != null && dp != null && dq != null && qi != null && p != null && q != null);
          } else if (JsonWebKeyType.EC.equals(kty) || JsonWebKeyType.EC_HSM.equals(kty)) {
              return (d != null);
          }
  
          return false;
      }
docs: Verifies whether the {@link JsonWebKey} has private key.
  
  @return true if the {@link JsonWebKey} has private key; false otherwise.