The GET /_matrix/key/v2/server/{keyId} endpoint is used to request signing
keys from remote homeservers, so that received events and incoming federation
requests can be validated.
The
specification
for this endpoint says that the keyId parameter is deprecated; however, it does
not say that the trailing slash may be omitted. The correct way to call this
endpoint is therefore as GET /_matrix/key/v2/server/.
This MSC contends that the trailing slash is redundant, and inconsistent with other endpoints, where we have recently made an effort to remove redundant trailing slashes (cf synapse#4935).
For background on the deprecation of keyId, see
matrix-doc#1423.
Synapse currently treats a request to GET /_matrix/key/v2/server (without the
trailing slash) the same as GET /_matrix/key/v2/server/ (and, in fact, all
requests to GET /_matrix/key/v2/server/{keyId}, with any keyId): it returns
all known signing keys for the local server.
In line with other endpoints which offer an optional URL path param
(example),
GET /_matrix/key/v2/server should be specified as a separate endpoint, whose
behaviour should be identical to that of GET /_matrix/key/v2/server/{keyId}
with an empty keyId parameter.
It's not entirely clear to me that the deprecation of keyId and the
recommendation to use the wildcard version of the endpoint is optimal, so an
alternative approach would be to reverse that deprecation and instead deprecate
the use of the wildcard lookup. However, that would be a more complex change
which is hard to justify at this point in the Matrix 1.0 release cycle.
None forseen. This is largely a formalisation of existing behaviour.
The trailing slash on GET /_matrix/key/v2/server/ is redundant. Let's clarify
that it is optional.