Pull Request resolves # .

• I read the Generative AI policy and my contribution is either not created with the help of AI or is compatible with the policy and GNU/GPL 2 or later.

Summary of Changes

Requires / depends on: #47985
Without that PR the language string is never loaded, so this change has no visible effect on its own.

The security log message of the "Authentication - Cookie" plugin is defined as:

PLG_AUTHENTICATION_COOKIE_ERROR_LOG_LOGIN_FAILED="Cookie login failed for user %u."

It is emitted in onUserAuthenticate() via
Text::sprintf('PLG_AUTHENTICATION_COOKIE_ERROR_LOG_LOGIN_FAILED', $results[0]->user_id).

The value passed in comes from #__user_keys.user_id, which actually holds the username (a string) — see onUserAfterLogin(), which stores $options['user']->username in that column. The %u specifier formats its
argument as an unsigned integer, so a (non-numeric) username is converted to 0 and the log always reads "… for user 0.", which does not identify the account.

This PR changes the placeholder from %u to %s so the actual username is logged. Only the en-GB source string is changed; other languages follow through the normal translation workflow.

Testing Instructions

Apply #47985 first, otherwise the
string stays untranslated and this change cannot be observed.

1. Enable the "Authentication - Cookie" plugin and make sure error logging is on (administrator/logs/everything.php, category security).
2. On the frontend, log in with "Remember Me" checked (creates a row in #__user_keys and a joomla_remember_me_* cookie).
3. In the browser dev tools, edit that cookie: change the part before the dot (the token), keep the part after the dot (the series) unchanged.
4. Reload a frontend page so the cookie authentication runs.
5. Look at the security entry in the log.

Actual result BEFORE applying this Pull Request

WARNING 127.0.0.1 security Cookie login failed for user 0.

Expected result AFTER applying this Pull Request

(the real username instead of 0)

Link to documentations

Please select:

• Documentation link for guide.joomla.org:

• No documentation changes for guide.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed