##
11.5.7 AbstractBasicAuthHandler Objects

`handle_authentication_request`(authreq, host, req, headers)
  Handle an authentication request by getting a user/password pair, and re-trying the request. authreq should be the name of the header where the information about the realm is included in the request, host is the host to authenticate to, req should be the (failed) `Request` object, and headers should be the error headers.