mod_auth_oauth_external: Allow different username in PLAIN vs final JID Mastodon for example having email addresses usernames in login, but a different username in the service itself. Thanks to @tcit@social.tcit.fr for the pointer to a usable validation endpoint for Mastodon, allowing this to be tested.

local count_registering = module:measure("user_registering", "rate");
local count_registered = module:measure("user_registered", "rate");

module:hook("user-registering", function ()
	count_registering();
end);

module:hook("user-registered", function ()
	count_registered();
end);