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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def proxy_fetch(self, env, url):
 """Proxy mode only endpoint that handles OPTIONS requests and COR fetches for Preservation Worker. Due to normal cross-origin browser restrictions in proxy mode, auto fetch worker cannot access the CSS rules of cross-origin style sheets and must re-fetch them in a manner that is CORS safe. This endpoint facilitates that by fetching the stylesheets for the auto fetch worker and then responds with its contents :param dict env: The WSGI environment dictionary :param str url: The URL of the resource to be fetched :return: WbResponse that is either response to an Options request or the results of fetching url :rtype: WbResponse """

        if not self.is_proxy_enabled(env):
            # we are not in proxy mode so just respond with forbidden
            return WbResponse.text_response('proxy mode must be enabled to use this endpoint',
                                            status='403 Forbidden')

        if env.get('REQUEST_METHOD') == 'OPTIONS':
            return WbResponse.options_response(env)

        # ensure full URL
        request_url = env['REQUEST_URI']
        # replace with /id_ so we do not get rewritten
        url = request_url.replace('/proxy-fetch', '/id_')
        # update WSGI environment object
        env['REQUEST_URI'] = self.proxy_coll + url
        env['PATH_INFO'] = env['PATH_INFO'].replace('/proxy-fetch', self.proxy_coll + '/id_')
        # make request using normal serve_content
        response = self.serve_content(env, self.proxy_coll, url)
        # for WR
        if isinstance(response, WbResponse):
            response.add_access_control_headers(env=env)
        return response