Create function to validate usernames (by regex)

web/src/base.php

@@ -73,3 +73,8 @@ function if_session_redirect_app() {
 	if (session() !== null)
 		redirect(APP_DIR);
 }
+
+
+function validate_username($username) {
+	return preg_match('/^[a-zA-Z0-9\_]+$/', $username);
+}