Push Gateway spec states that valid Pusher URLs are more flexible than they really are

[callahad]

The Push Gateway spec states:

Notifications are sent to the URL configured when the pusher is created. This means that the HTTP path may be different depending on the push gateway.

However, the Client-Server API Spec began asserting that the pusher URL "must have a path of /_matrix/push/v1/notify" with version 0.4.0 in August 2018. The change itself was introduced by matrix-org/matrix-spec-proposals#1522.

Thus, the HTTP path cannot be different depending on the push gateway; only the host is allowed to differ.

Synapse began enforcing this restriction in 1.25.0 with the merge of matrix-org/synapse#8865, but the discrepancy between the Push Gateway spec and the Client-Server API spec has caused confusion with real-world Matrix deployments.

The language in the Push Gateway spec ("the HTTP path may be different") predates matrix-org/matrix-spec-proposals#1522, and I suspect it was simply overlooked when reviewing that change.

[richvdh]

See also matrix-org/matrix-spec-proposals#2970 which proposes relaxing the requirement on the pusher URL.