ntfy credentials support?

[shaohme]

The ntfy (https://ntfy.sh/) server implements authentication and ACLs to secure its push messages.
Matrix Synapse homeserver currently supports it well, but without authentication.

The ntfy configuration (https://docs.ntfy.sh/config/?h=access#access-control-list-acl) manual states that administrator could allow anonymous (everyone/) to have write access to "up*" topics while having auth-default-access: "deny-all" to mitigate this problem.

A user expressed this issue at binwiederhier/ntfy#1034

Have synapse developers considered this issue, like allowing configured credentials for ntfy server, or should this problem be addressed otherwise, like the Element X client announcing to synapse which credentials synapse should use to notify with?

Maybe this is a non-issue for most people. I just got curious ...

[reivilibre]

Synapse doesn't actually have any built-in support for ntfy, it's more the other way around: Synapse sends out push notifications using the Push Gateway API which ntfy supports (https://github.com/binwiederhier/ntfy/blob/630f2957deb670dcacfe0a338091d7561f176b9c/server/server_matrix.go#L108).

Supporting ntfy auth is therefore a little bit tricky.

The ntfy manual's approach seems most sensible to me — reserve a namespace (the up* topics) for UnifiedPush usage and then allow anyone to send to those. Since the topic name should be long and random (secret), this is as good as authenticated.

If it's really considered necessary that any additional authentication is needed I suspect the right place to add it would be the Ntfy client and the Ntfy server, sending it through the pushkey or the data (PusherData) payload. (I do appreciate this is awkward for Ntfy since it's trying to be a generic mechanism, but it already needs special Matrix support and pragmatically this seems the most viable way to do this.)
That said: Do you really want to give your own ntfy credentials to your homeserver (Synapse), which might be operated by someone else (that you don't trust with your ntfy credentials)?
Having a single-purpose random token (the up* topic) actually seems better for security anyway.

[shaohme]

Thanks. That covers it for me :-)