mod_http_oauth2: Enforce response type encoded in client_id The client promises to only use this response type, so we should hold them to that. This makes it fail earlier if the response type is disabled or the client is trying to use one that it promised not to use. Better than failing after login and consent.

This module logs events where more than a certain amount of CPU time was
spent.

``` lua
log_cpu_threshold = 0.01 -- in seconds, so this is 10 milliseconds
```

Uses the Lua
[`os.clock()`](http://www.lua.org/manual/5.2/manual.html#pdf-os.clock)
function to estimate CPU usage.