[HTTP/3] SNI does not use the Host header value #57169
Description
HttpClient HTTP/3's implementation does not use HttpRequestMessage.Headers.Host for SNI, unlike prior HTTP versions.
var request = new HttpRequestMessage(HttpMethod.Get, "https://localhost:443/");
request.Version = HttpVersion.Version30;
request.VersionPolicy = HttpVersionPolicy.RequestVersionExact;
request.Headers.Host = "testhost";Expected SNI: "testhost"
Actual SNI: "localhost"
Priority: Medium, common customer requirement, difficult to work around.