Allow + in WordPress Usernames

gistfile1.txt

/*
	Allow + in usernames

	Just add this code to your active theme's functions.php or a custom plugin.
*/
function pmprorh_sanitize_user( $username, $raw_username, $strict = false ) 
{			
	//only check if there is a + in the raw username
	if(strpos($raw_username, "+") === false)
		return $username;
	
	//start over
	$username = $raw_username;
	
	$username = wp_strip_all_tags( $username );
	$username = remove_accents( $username );
	// Kill octets	
	$username = preg_replace( '|%([a-fA-F0-9][a-fA-F0-9])|', '', $username );
	$username = preg_replace( '/&.+?;/', '', $username ); // Kill entities

	// If strict, reduce to ASCII for max portability.
	if ( $strict )
		$username = preg_replace( '|[^a-z0-9 _.\-@\+]|i', '', $username );		//added a + here
		
	$username = trim( $username );
	// Consolidate contiguous whitespace
	$username = preg_replace( '|\s+|', ' ', $username );

	return $username;
}
add_filter("sanitize_user", "pmprorh_sanitize_user", 1, 3);