Maybe https://ntfy.sh https://ntfy.sh ? It's a generic pub/sub tool that can provide a clickable link on a mobile app back to a service. It's covers the "self-

Maybe https://ntfy.sh https://ntfy.sh ? It's a generic pub/sub tool that can provide a clickable link on a mobile app back to a service. It's covers the "self-hosted & open source" but it's not specifically an authentication thingy, so you would have to generate the auth factor to push and the service that verifies it, like a web hook.