mod_http_oauth2: Refactor client grant and response type checks Iterating over an array instead of creating a Set ought to create fewer short-lived tables. The arrays are usually very short so shouldn't be a performance issue. Moves validation earlier as to do less work before discovering that it can't proceed anyway.

This module blocks configured queries that change server state.

E.g. to make vCard storage read-only:

``` lua
readonly_stores = {
	vcard = { "vcard-temp", "vCard" };
}
```