mod_sasl2: Pull user-agent info into sasl_handler for later reference It may be of interest to post-auth things. Putting it on the session was another option considered, but that seemed unnecessary overhead for something that might be rarely used. sasl_handler is cleared after successful authentication.

This module blocks configured queries that change server state.

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

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