Invite spam control (SPEC-96)

[matrixbot]

See SPEC-60 for room knock support.

There are outstanding issues with inviting users to rooms, namely:

• Clients need to know why they are being invited (e.g. a reason key, just like for kicks/bans). However, this opens up a spam vector where any user can send any other user a string. Do we really want to do that?
• It may be useful to send other state information such as the room name, topic, etc. How is this specified in this request? Does the inviter even specify this, or is it a room config option which fields are shared? This has a lot of parallels with the published room API which exposes some state events.
  • How do we prevent spam attacks via the room name/topic? The spam attack vector may be something we're just going to have to deal with. Ultimately, we need to expose more data about the room. This data is going to be set by the client. Compromises like "just give the event type" don't really fix the problem "because.my.event.type.could.be.like.this".

(Imported from https://matrix.org/jira/browse/SPEC-96)

(Reported by @kegsay)

[matrixbot]

Jira watchers: @kegsay

[matrixbot]

Links exported from Jira:

relates to SPEC-60

[richvdh]

SPEC-60 now at #932

[heyakyra]

I see in SPEC-96 "Clients need to know why they are being invited (e.g. a reason key, just like for kicks/bans). However, this opens up a spam vector where any user can send any other user a string. Do we really want to do that?"

One way to manage this is to give control over how and where users may send invites from. For example, maybe I don't want to be able to be contacted directly/out of nowhere, but if you are in a room with me, then you may.

So an imperfect solution i've thought of is to have a way to know and display where the user was invited from. This way there is at least some context to understand how the user was discovered or the inviting party is connected. This possibly could be implemented through forcing room invitations to be whispers in other rooms (and possibly giving each user their own "room" from which they can either allow or deny whispers): https://github.com/vector-im/riot-web/issues/3345#issuecomment-285274081

A simpler but less ideal option is to have a way to always show the rooms users have in common with each other, which I believe discord does.

[madduck]

Please see my comment at #2339 (comment)

[Bandie]

I have a similar approach like @heyakyra.
See synapse issue vector-im/element-web#9261

[richvdh]

I don't think there's much left to do here. Invites can now come with reasons (#2795), and invites already come with a "stripped state" including room name etc. In short, this issue is showing its age.