maybe u can help to solve this problem.
for example i have this link

https://direktoriku.com/shopping/?user=

and i want to add username after login, like https://direktoriku.com/shopping/?user=admin

I want to make it on button.

<a href="https://direktoriku.com/shopping/?user=username">
    <button>Click me</button>
</a>

I want to put this on post / page.