Unable to run ASP.NET Core application with HTTP/3 enabled on a Plesk server

Symptoms

• A working ASP.NET Core application stops working after enabling HTTP/3 as per documentation with errors 400 and 499.

Cause

The issue is related to the bug PPPM-14435: HTTP/3 breaks phusion passenger implementation of .NET toolkit.

Resolution

Until the bug is fixed, there is one workaround:

1. Connect to the server via SSH

2. Edit file /etc/nginx/plesk.conf.d/vhosts/example.com.conf (where example.com is the affected domain)

3. Add the Host line as such:

   #extension dot-net begin
   location / {
   passenger_enabled on;
   passenger_set_header Host $host:$server_port;

4. Save the file and restart nginx:

   # systemctl restart nginx