I'm probably not understanding a key piece of technical info about the 
protocol, but when I see this statement it makes me think it has similar issues 
to tls-sni-01.  If we're relying on the hosting provider enforcing certain 
constraints like this, then we're delegating a critical piece of domain control 
back to the hosting provider which would be a no-go.

4.  Security Considerations

   The design of this challenges relies on some assumptions centered
   around how a server behaves during validation.

   The first assumption is that when a server is being used to serve
   content for multiple DNS names from a single IP address that it
   properly segregates control of those names to the users on the server
   that own them.  This means that if User A registers Host A and User B
   registers Host B the server should not allow a TLS request using a
   SNI value for Host A that only User A should be able to serve that
   request.  If the server allows User B to serve this request it allows
   them to illegitimately validate control of Host A to the ACME server.

Please let me know what I'm missing.


> -----Original Message-----
> From: Acme [mailto:acme-boun...@ietf.org] On Behalf Of Roland Bracewell
> Shoemaker
> Sent: Friday, February 23, 2018 3:00 AM
> To: Rich Salz <rs...@akamai.com>
> Cc: IETF ACME <acme@ietf.org>; Martin Thomson
> <martin.thom...@gmail.com>
> Subject: Re: [Acme] ALPN based TLS challenge
> Here is the ID: https://datatracker.ietf.org/doc/draft-shoemaker-acme-tls-
> alpn/
> > On Feb 22, 2018, at 8:38 PM, Salz, Rich <rs...@akamai.com> wrote:
> >
> > Yes, like Martin said, submit the individual draft and we can call for 
> > adoption.
> >
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