Is it possible to have a URL only be accessible through a portal?

Question

I've got a website that requires a login, this website shows a "portal" which makes it possible to go to deluge/plex/sonarr (webapps). these apps are connected to ports. so example.com:83031 = plex and example.com:83032 is sonarr (as an example).

Now if I go to example.com it prompts me a login and I if I then click on "plex", the portal goes to example.com:83031. this is correct. however, is there a way to disable a direct link to example.com:83031 (so is there a way to ONLY make it able to enter that site through portal?)

Long story short: I want example.com:83031 to ONLY be available through the portal, not if you enter it directly into the browser. is this possible?

[Editted the domains, got the point!]

Answer 1

Using reverse-proxy on Apache has fixed this issue.

Picture describing the outcome

Answer 2

In theory, a browser should send a "redirect" indicating from where you came. Hence, example.com:83031 could check if you came from example.com:80. This is however not reliable.

However, if you redirect to example.com:83031/loginOK?<GUID> then you have explicitly encoded the redirection information, in a way that no browser can strip.

BTW, don't invent non-existent domains. example.com exists for a reason.