Change:
port and, if successful, send HTTP requests using the mapping described in this document. <del> Connectivity problems (e.g. firewall blocking UDP) can result in QUIC connection establishment failure, in which case the client SHOULD continue using the existing connection or try another alternative endpoint offered by the origin. </del> <ins> 3.2.2. Although HTTP is independent of the transport protocol, the "http" scheme associates authority with the ability to receive TCP connections on the indicated port of whatever host is identified within the authority component.  Because HTTP/3 does not use TCP, HTTP/3 cannot be used for direct access to the authoritative server for a resource identified by an "http" URI.  However, protocol extensions such as ALTSVC permit the authoritative server to identify other services which are also authoritative and which might be reachable over HTTP/3. </ins> <del> Servers MAY serve HTTP/3 on any UDP port, since an alternative always includes an explicit port. </del> <ins> Prior to making requests for an origin whose scheme is not "https", the client MUST ensure the server is willing to serve that scheme. If the client intends to make requests for an origin whose scheme is "http", this means that it MUST obtain a valid "http-opportunistic" response for the origin as described in RFC8164 prior to making any such requests.  Other schemes might define other mechanisms. </ins> 3.3.

Discussion:
Clients MAY establish QUIC connections using the host and port indicated in the URL for "https" URLs only Non-"https" origins are able to be delegated using Alt-Svc Cribs a lot of text from .
Are we waiting on a consensus call for this?
The call has been issued and is running until Saturday UTC. If you have comments, please make them now!
Excellent! Can't wait for this to land. (Looks like I need to finish reading my WG email :>)
NAME I'll get your comments as a separate PR.
S 2.4. This text seems quite a bit more restrictive than S 9.1.1. of RFC 7540, which just allows reuse as long as the SAN is present in the cert. Is that intentional?
I think that the intent was to present equivalent text. Though the thinking about coalescing has evolved some in the meantime. We should discuss where we think the state of this discussion is at and see if we can capture something sensible.
Yes, it'd be good to capture something more up-to-date if we can come to consensus on that. Is explicit signal meant to indicate DNS and/or ORIGIN frame? If so, maybe call those two out as examples?
NAME I think the dilemma is that some of those things don't exist yet for H3. For example, Mike did some earlier work to redefine ALTSVC frame for H3 but there is yet to be equivalent for ORIGIN or secondary certs.
Yes, it's intentional. RFC7540 allows coalescing based on the cert and DNS, because you're connected to the authoritative origin. However, HTTP/3 is never connected on the authoritative endpoint for an http(s?):// URL, so you need something else to tell you that's okay. This could be an Alt-Svc record for that origin delegating to the same UDP port. This could be an ORIGIN-for-H3 frame telling you to throw caution to the wind and trust the cert, if the client thinks that's sensible.
Discussed in London; also blocked on URL defining how a client decides which connection / server to ask for a given resource.
Discussed in ZRH. Waiting for HTTP changes to materialize.