Do I need need to change application code to track User ID?

There is probably a simple YES/NO answer to this, alhough I spent a few hours reading documentation and testing all sorts of js code - nothing works. I am not a coder, though trying to undrerstand the more technical bits as well.

My question is: can I simply use Piwik to record user_ID from the aplication as reported in the browser when looking at source code?
I have no access to the application and there is no way I can define variables or set permissions there, but I can see the user_ID right in the browser.

How do I get this user_ID into Piwik from the application header?

I tried to read it using custom variable, but Piwik simply diplayed it as “user_ID” text, rather then the actual value “123”. I understand that the actual variable for user ID is in the cookie, which is encrypted and inaccessible to Piwik, so how is it possisble to report it without adding Piwik code into the appllication?

Other than that Piwik is looking great and I am really excited to see the whole world of new users on the map :slight_smile:

Many thanks.

I think I got it to work! Thanks to this post:
I simply had to type the variable name without any quotes or $ sign.

Just for the record: it is working via custom variable, but the same variable when passed into User ID function is not working.