MSC3288: Add room type to /_matrix/identity/v2/store-invite API

proposals/3288-pass_room_type_in_3pid_invite.md

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+# MSC3288: Add room type to `/_matrix/identity/v2/store-invite` API
+
+Currently when inviting via 3pid, the Identity Server receives some information about the room,
+like for example the room name and avatar as well as the inviter name.
+This allows the identity server to generate a rich email to the invitee.
+
+Now that the matrix spec supports spaces, it would be nice to also provide this information to the identity server
+so that the email invite could be customized for spaces.  The current implementation would say wrongly that 
+you are invited to a room when the room is actually a space.
+
+The goal of this proposal is to make 3pid invites space aware.
+
+
+## Proposal
+
+Homeservers should also send the `room_type` to the identity server when performing a third party invite (__Invitation storage__).
+
+
+__Proposed change:__
+
+Add a new `room_type` field in json body of [`POST /_matrix/identity/v2/store-invite`](https://matrix.org/docs/spec/identity_service/r0.3.0#post-matrix-identity-v2-store-invite):
+
+| Parameter | Type | Description |
+|--|--|--|
+| room_type  | string  | The room type for the room to which the user is invited. This should be retrieved from the value of `type` in the `m.room.create` event's `content`. Do not include parameter if `type` is not present in `m.room.create`.
+
+````
+POST /_matrix/identity/v2/store-invite HTTP/1.1
+Content-Type: application/json
+
+{
+  "medium": "email",
+  "address": "foo@example.com",
+  "room_id": "!something:example.org",
+  "sender": "@bob:example.com",
+  "room_alias": "#somewhere:exmaple.org",
+  "room_avatar_url": "mxc://example.org/s0meM3dia",
+  "room_join_rules": "public",
+  "room_name": "The Bob Project",
+  "room_type": "m.space",
+  "sender_display_name": "Bob Smith",
+  "sender_avatar_url": "mxc://example.org/an0th3rM3dia"
+}
+````
+
+The identity server could then use room type to customize the email depending on the room type.
+
+__Email Generation__
+
+The link in the generated email should also pass over the `room_type` to clients ( like it is doing for 
+`inviter_name`, `room_name`, `room_avatar`)
+
+## Potential issues
+
+None.
+
+
+## Security considerations
+
+None.
+
+## Unstable prefix
+
+The following mapping will be used for identifiers in this MSC during development:
+
+
+Proposed final identifier       | Purpose | Development identifier
+------------------------------- | ------- | ----
+`room_type` | POST body | `org.matrix.msc3288.room_type`