At my work, we are finally upgrading our old Identity Server 3 to 4. We just got a very weird problem doing so. Everything works fine in all major browsers, but we also need to support some Electron clients. Here is where the weird part begins. All very old clients using Electron version 3 still work. All newer clients starting at Electron 9 also work. The only clients that don't work are the ones using Electron 6 (Chrome 76).
I already found this very helpful article written by Sebastian Gingter which helped to get the login working. But it only got me one step further. Now the client gets stuck at the connect/authorize/callback endpoint using the response_mode = form_post.
I already found some articles/stackoverflow questions pointing out to check the redirect URIs and to downgrade the CSP to version 1. The redirect URIs are configured correctly since the other clients work. The CSP does not help since I don't even get that far. It seems that the response body is never even loaded by Electron/Chrome.
The request never finishes. On the server-side, it does though. I debugged through the IS 4 code and the dynamic HTML is written to the response like with all the other clients. I even called CompleteAsync() on the response manually and it still did not finish.
I researched and debugged for quite some time now and am out of ideas. Does anyone out there know this issue and more importantly also knows how to fix it?