Allow our application (currently on subdomain) to be served from our regular domain URL.

We have a chat application that is installed on another server and is installed on a subdomain. (for example: [login to view URL]) The chat application is fully mobile responsive already. However, we want to place it on our main root domain (for example: [login to view URL]). So when a desktop user goes to the root domain page, he sees the header and footer and the chat application served in an iframe. This part is easy. However, for a mobile user, we want him to see a button to log into our chat application. When he clicks this button it will open a new page, with our chat application on the new page. However, this new page must still have the original root domain attached to it. You can use a new subpage if needed (for example: [login to view URL]) But the important point is we do not want the browser URL to point to https://chatapp.mydomain.com. We want it to be pointing to [login to view URL]) This will most likely have to be placed in an iframe in some way within a new subpage. The page will still be fully responsive. I have an example website to show that this can be done. It may or may not require the use of PHP instead of standard HTML. I am not sure. Please only apply if you can do this properly.