Thanks for checking!
I was actually testing an invalid login, where it says "connection error" instead of "invalid login credentials" because the backend error isn't sent due to a CORS issue.
After attempting login with piefed.social vs feddit.online, here's the screenshots. See the "CORS missing origin" error under trasnferred column for feddit.online. Also the lack of access-control-allow-* headers compared to piefed.social.
That’s actually incorrect, it is a solved problem in voyager. Clicking the link in the post from any Lemmy instance, or up to date piefed instance like piefed.blahaj.zone, opens in app.
The only reason it doesn’t work from piefed.ca is piefed.ca is running an outdated version of Piefed that doesn’t support the federated instances endpoint in api/alpha.
Proof:
https://piefed.ca/api/alpha/federated_instances
https://piefed.social/api/alpha/federated_instances