mod_client_management: Add support for revocation of clients (when possible) We decided to keep the unified listing of "clients", which includes both SASL2 clients and OAuth grants, etc. To a user, or someone wanting to manage what can access their account, they are largely equivalent. To accomplish this technically, we add a prefix to the id to state what type it really is.

This module lets you block connections to any remote servers not on a
whitelist.

``` {.lua}
modules_enabled = {
    -- other modules --
    "s2s_whitelist",

}
s2s_whitelist = {
    "example.org",
}
```