mod_rest: Reject password that fails saslprep earlier (thanks tgy) Prevents an error later if/when passing the password through saslprep a second time in the authentication module, since the prep functions now reject nil The error reporting could be improved but that would involve adding a way to pass errors back out of the check_credentials() function.

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",
}
```