matrix-spec-proposals/content/client-server-api/modules/guest_access.md

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Guest Access

There are times when it is desirable for clients to be able to interact with rooms without having to fully register for an account on a homeserver or join the room. This module specifies how these clients should interact with servers in order to participate in rooms as guests.

Guest users retrieve access tokens from a homeserver using the ordinary register endpoint, specifying the kind parameter as guest. They may then interact with the client-server API as any other user would, but will only have access to a subset of the API as described the Client behaviour subsection below. Homeservers may choose not to allow this access at all to their local users, but have no information about whether users on other homeservers are guests or not.

Guest users can also upgrade their account by going through the ordinary register flow, but specifying the additional POST parameter guest_access_token containing the guest's access token. They are also required to specify the username parameter to the value of the local part of their username, which is otherwise optional.

This module does not fully factor in federation; it relies on individual homeservers properly adhering to the rules set out in this module, rather than allowing all homeservers to enforce the rules on each other.

Events

{{m_room_guest_access_event}}

Client behaviour

The following API endpoints are allowed to be accessed by guest accounts for retrieving events:

• GET /rooms/:room_id/state
• GET /rooms/:room_id/context/:event_id
• GET /rooms/:room_id/event/:event_id
• GET /rooms/:room_id/state/:event_type/:state_key
• GET /rooms/:room_id/messages
• GET /rooms/:room_id/members
• GET /rooms/:room_id/initialSync
• GET /sync
• GET /events as used for room previews.

The following API endpoints are allowed to be accessed by guest accounts for sending events:

• POST /rooms/:room_id/join
• POST /rooms/:room_id/leave
• PUT /rooms/:room_id/send/m.room.message/:txn_id
• PUT /sendToDevice/{eventType}/{txnId}

The following API endpoints are allowed to be accessed by guest accounts for their own account maintenance:

• PUT /profile/:user_id/displayname
• GET /devices
• GET /devices/{deviceId}
• PUT /devices/{deviceId}

The following API endpoints are allowed to be accessed by guest accounts for end-to-end encryption:

• POST /keys/upload
• POST /keys/query
• POST /keys/claim

Server behaviour

Servers MUST only allow guest users to join rooms if the m.room.guest_access state event is present on the room, and has the guest_access value can_join. If the m.room.guest_access event is changed to stop this from being the case, the server MUST set those users' m.room.member state to leave.

Security considerations

Each homeserver manages its own guest accounts itself, and whether an account is a guest account or not is not information passed from server to server. Accordingly, any server participating in a room is trusted to properly enforce the permissions outlined in this section.

Homeservers may want to enable protections such as captchas for guest registration to prevent spam, denial of service, and similar attacks.