mod_http_oauth2: Create proper template for OOB code delivery This also improves security by reusing the security and cache headers, where mod_http_errors/http-message doesn't add such headers. Colors selected by taking rotating the error colors, rrggbb -> ggbbrr

This module helps make BOSH and WebSocket connection endpoints
discoverable via the HTTP method described in
[XEP-0156](https://xmpp.org/extensions/xep-0156.html#http).