code: def get_cas_client(service_url=None, request=None):
      
      # Handle CAS_SERVER_URL without protocol and hostname
      server_url = django_settings.CAS_SERVER_URL
      if server_url and request and server_url.startswith('/'):
          scheme = request.META.get("X-Forwarded-Proto", request.scheme)
          server_url = scheme + "://" + request.META['HTTP_HOST'] + server_url
      # assert server_url.startswith('http'), "settings.CAS_SERVER_URL invalid"
  
      if not django_settings.CAS_VERIFY_SSL_CERTIFICATE:
          warnings.warn(
              "`CAS_VERIFY_SSL_CERTIFICATE` is disabled, meaning that SSL certificates "
              "are not being verified by a certificate authority. This can expose your "
              "system to various attacks and should _never_ be disabled in a production "
              "environment."
          )
  
      return CASClient(
          service_url=service_url,
          version=django_settings.CAS_VERSION,
          server_url=server_url,
          extra_login_params=django_settings.CAS_EXTRA_LOGIN_PARAMS,
          renew=django_settings.CAS_RENEW,
          username_attribute=django_settings.CAS_USERNAME_ATTRIBUTE,
          proxy_callback=django_settings.CAS_PROXY_CALLBACK,
          verify_ssl_certificate=django_settings.CAS_VERIFY_SSL_CERTIFICATE
      )
docs: initializes the CASClient according to
      the CAS_* settigs