mod_http_oauth2: Do not enforce PKCE on Device and OOB flows PKCE does not appear to be used with the Device flow. I have found no mention of any interaction between those standards. Since no data is delivered via redirects in these cases, PKCE may not serve any purpose. This is mostly a problem because we reuse the authorization code to implement the Device and OOB flows.

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).