<?php
/*
Plugin Name: Disable Registrations
Description: This plugin disables access to registration.php and blocks any registrations.
Plugin URI:  http://simonwheatley.co.uk/bbpress/disable-registrations
Author: Simon Wheatley
Author URI: http://simonwheatley.co.uk/
Version: 0.1
*/

// Fires every time bbPress inits, a bit ick but it's super quick string ops
// (which is what PHP is good at).
function da_disable_registrations()
{
	// Shame there isn't a hook to grab before the new user is registered on register.php
	// In the absence of that, we will check whether we're on register.php
	if ( ! da_str_ends_with( strtolower( $_SERVER[ 'PHP_SELF' ] ), 'register.php' ) ) return;
	// We are on register.php? Stop executing (with a message).
	bb_die( "Registration is not allowed on this website. Please contact the site administrators." );
	exit; // Never reached, unless bb_die fails for some freaky reason
}

// Checks whether string a ends with string b
function da_str_ends_with(& $str, $end)
{
	return ( substr( $str, - strlen( $end ), strlen( $end ) ) == $end );
}

add_action( 'bb_init', 'da_disable_registrations' );

?>

Trent