def sign(jwk, plain_text, header = nil)
      protected_binary = JOSE.urlsafe_encode64(to_binary)
      payload = JOSE.urlsafe_encode64(plain_text)
      signing_input = signing_input(plain_text, protected_binary)
      signature = JOSE.urlsafe_encode64(alg.sign(jwk, signing_input))
      return signature_to_map(payload, protected_binary, header, jwk, signature)
    end
def sign(jwk, plain_text, header = nil)
      protected_binary = JOSE.urlsafe_encode64(to_binary)
      payload = JOSE.urlsafe_encode64(plain_text)
      signing_input = signing_input(plain_text, protected_binary)
      signature = JOSE.urlsafe_encode64(alg.sign(jwk, signing_input))
      return signature_to_map(payload, protected_binary, header, jwk, signature)
    end
Signs the `plain_text` using the `jwk` and algorithm specified by the `jws`.
 @see JOSE::JWS.sign
 @param [JOSE::JWK] jwk
 @param [String] plain_text
 @param [JOSE::Map, Hash] header
 @return [JOSE::SignedMap]