Synapse accepts "user" instead of "username" in application service /register

[neilalexander]

Description

When an AS registers a user in Synapse, it seems happy to accept "user" instead of the specced "username" in the request body.

This is related to matrix-org/sytest#1017.

Steps to reproduce

Up until matrix-org/sytest@ab7b8f0, Sytest was testing this way and the tests passed.

Version information

• Version: Seemingly all versions

[anoadragon453]

This may be related to old client behaviour, in which case changing it would be hard.

[richvdh]

possibly, but it would have to be very old clients, and tbh we should be doing a better job at deprecating and sunsetting these things.

[clokep]

I'm assuming that this accepts both since sytest still passes? So this is really a matter of deprecating the old user field?

[anoadragon453]

@clokep Yep. We need to do a similar thing to #9559 / #9548 here. Create a deprecation notice in the changelog and then remove the old support once enough time has passed.

Someone needs to do the investigation on whether anyone is still using user as well (a good way to do so is via grepping matrix.org logs). Nevermind, this is in the body of the request, which is not logged.

[clokep]

Note that #927 seems to have added a fallback to "username". I think this is really Synapse accepts "user" in addition to "username" FWIW (at least since #927).

[clokep]

@Half-Shot / @tulir Any idea if we can deprecate and remove this (similar to the legacy AS paths)?

[clokep]

And for all avoidance of doubt that this is really old:

• Added in matrix-org/matrix-spec@8e75c5e
• Removed in matrix-org/matrix-spec@9cb6269

So this was way before r0.1.0 of the appservice spec.

I'm going to do a PR to deprecate this and we can remove it in the future.

[clokep]

This is deprecated and can be removed in v1.88.0. Since this was never specced I think we can just remove it.