Reading all response header information from okta-auth

I am trying to read rate-limit values from response header . I am trying to read the values from okta-auth library , but it returns only basic header information and not the header x-rate-limit-limi(it is returned as null) . CORS is enabled for website .I tried printing the header values from okta-auth library file jqueryRequest.js , even there the values had only basic header information.Could you suggest if am missing something ?