mod_auth_oauth_external: Expect XEP-0106 escaped username in PLAIN This allows entering an email address as username in some clients by escaping the @ as \40, enabling authentication against Mastodon

This module blocks configured queries that change server state.

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

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