How to subscript external task

Hi, I’m trying to subscribe external task topic by javascript and use camunda-bpm-identity-keycloak to identify user.
But polling failed.
polling failed with TypeError: Cannot read property ‘statusCode’ of undefined.

I print the Exception. Then I found the cause is self signed certificate problem.
GotError: self signed certificate.
But there is no parameter to set certificate when I use KeycloakAuthInterceptor.