Fixes#10416
Followup to a hardcoded string in [gitea#17743](https://github.com/go-gitea/gitea/pull/17743)
* instead of using a hardcoded namespace, use the configured application domain
* `ssh-keygen` refuses to work with empty namespace, but `Domain` falls back to `localhost`:
95dca7ff57/modules/setting/server.go (L192)
* since `VerifySSHKey` verifies the namespace, I think that using a mostly-unique string instead of a hardcoded one doesn't hurt. Here's what `man ssh-keygen` says on the topic:
> An additional signature namespace, used to prevent signature confusion across different domains of use (e.g. file signing vs email signing) must be provided via the -n flag. Namespaces are arbitrary strings, and may include: “file” for file signing, “email” for email signing. For custom uses, it is recommended to use
names following a NAMESPACE@YOUR.DOMAIN pattern to generate unambiguous namespaces.
## Testing
There's a test `TestFromOpenSSH` but it uses a hardcoded default namespace `file`:
95dca7ff57/models/asymkey/ssh_key_test.go (L334)
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/10429
Reviewed-by: Beowulf <beowulf@beocode.eu>
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: 0ko <0ko@noreply.codeberg.org>
Co-committed-by: 0ko <0ko@noreply.codeberg.org>
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