Custom URI Scheme (fates://) browser redirect failing for Steam Game (Might & Magic Fates) on KDE Plasma*

Ask Fedora
,
1

Environment:

  • OS: Fedora KDE Plasma
  • Game: Might & Magic Fates (Steam AppID 3918850)
  • Browsers Tested: Firefox, Google Chrome (RPM)
  • Proton Versions Tested: Experimental

The Problem: I am trying to play Might & Magic Fates, which requires a web-based authentication to log in. When clicking “Login” in the game, it opens my default web browser. After successfully authenticating on the web page, the browser attempts to redirect back to the game using a custom URI scheme (fates://callback...).

However, the automated handoff fails. The browser does not trigger the game, and the authentication token is never passed back to the Steam process.

What I Have Tried (Troubleshooting Steps):

1. Identified the Custom Schema & Manually Registered a Handler I intercepted the redirect URL and found it uses the fates:// protocol. Because Fedora didn’t have a handler for this, I manually created a .desktop entry:

nano ~/.local/share/applications/mm-fates-handler.desktop

Ini, TOML[Desktop Entry] Type=Application Name=Might and Magic Fates Handler Exec=/usr/bin/steam "steam://run/3918850//%u" StartupNotify=false MimeType=x-scheme-handler/fates;

2. Registered the MimeType I bound the protocol to the new handler and updated the KDE application cache:

Bashxdg-mime default mm-fates-handler.desktop x-scheme-handler/fates update-desktop-database ~/.local/share/applications kbuildsycoca6

3. Verified Terminal Handoff (This Works!) If I copy the callback URL from the browser and manually run it through xdg-open in the terminal, wrapped in quotes, it successfully triggers Steam and logs me into the game:

Bashxdg-open "fates://callback&state=[TOKEN]&scope=openid+offline_access..."

The Bottleneck / Where I Need Help: Even though xdg-open works perfectly from the terminal (it open the game from start using steam but don’t pass argument), the native browser redirect still fails to trigger the prompt to open the application, so the game never log in .

**some of this generated using ai after trying it to solve the problem .
**I appreciate any help , thank you in advance .