Turn HTTP/3 on by default in Kestrel

[JamesNK]

Fixes #36486

[Tratcher]

Should we try to fix #41762 first? Will devs get errors if they try this and the cert doesn't work? Or will it fall back silently?

[JamesNK]

It falls back silently.

[ghost]

@JamesNK, this change will be considered for inclusion in the blog post for the release it'll ship in. Nice work!

Please ensure that the original comment in this thread contains a clear explanation of what the change does, why it's important (what problem does it solve?), and, if relevant, include things like code samples and/or performance numbers.

This content may not be exactly what goes into the blog post, but it will help the team putting together the announcement.

Thanks!

[Eagle3386]

@JamesNK I'm a bit confused: while it does state Merged into main since almost a year ago, even the current main-branch as of now still hasn't enabled HTTP/3 in Kestrel by default:

aspnetcore/src/Servers/Kestrel/Core/src/ListenOptions.cs

Line 19 in c1b7624

internal const HttpProtocols DefaultHttpProtocols = HttpProtocols.Http1AndHttp2;

Furthermore, if I explicitly go to the commit's "branch", it reads as follows:

This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.

Therefore, I'd like to know what happened & what's the plan for going forward with Kestrel & "HTTP/3 on by default"?

[JamesNK]

It was later turned off by default because anti-virus would always prompt for HTTP/3 endpoints.

You can still configure Kestrel to turn HTTP/3 on if you want to use it.

[Eagle3386]

Thanks, but are there plans to re-enable this by default at some future point (.NET 9/10) or will it remain like it's now?