From: Stuart Henderson <stu@spacehopper.org>
Subject: Re: [PATCH] ssh-add: Support @ in the user part of destination constraints
To: Max Zettlmeißl <max@zettlmeissl.de>
Cc: Damien Miller <djm@mindrot.org>, "Todd C. Miller" <millert@openbsd.org>, tech@openbsd.org
Date: Fri, 6 Sep 2024 19:40:25 +0100

On 2024/09/06 18:21, Max Zettlmeißl wrote:
> On Fri, 6 Sept 2024 at 04:16, Damien Miller <djm@mindrot.org> wrote:
> > The only problem is that someone, somewhere, somehow will have used '@'
> > in a hostname and this will break them.
> 
> Now we both know that this will not prevent anyone out there from
> using it, but isn't an '@' in a hostname formally invalid?
> RFC 952 and 1123 specify \-0-9A-Za-z and essentially A-Z is treated as
> a-z and the period separates components. The hostname also may not
> start with a hyphen.

An hostname as considered by ssh isn't necessarily a DNS hostname,
for example people use aliases in .ssh/config. This does work for
some chars not allowed in DNS, but I haven't been able to persuade
it to work with @.