Merge pull request #2765 from matrix-org/travis/msc/widget-avatars

MSC2765: Widget avatars

proposals/2765-widget-avatars.md

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+# MSC2765: Widget avatars
+
+Currently widgets have a name and title associated with them, though no opportunity for avatars
+for a favicon-like experience. This proposal introduces such a concept.
+
+## Proposal
+
+A new optional paramater named `avatar_url` is added to the widget definition. This parameter is
+an MXC URI to an image clients can use to associate with the widget, likely alongside the `name`
+and/or `title`.
+
+Widget avatars SHOULD be legible at small sizes, such as 20x20. The MXC URI in the `avatar_url`
+should be the source material to allow clients to use the `/thumbnail` API to get a size for their
+use case.
+
+Rendering avatars is optional for clients, much like how clients are not required to use the `name`
+or `title` of a widget.
+
+An example widget would be:
+
+```json
+{
+    "creatorUserId": "@alice:example.org",
+    "data": {
+        "custom_key": "This is a custom key",
+        "title": "This is a witty description for the widget"
+    },
+    "id": "20200827_WidgetExample",
+    "name": "My Cool Widget",
+    "type": "m.custom",
+    "url": "https://example.org/my/widget.html?roomId=$matrix_room_id",
+    "waitForIframeLoad": true,
+    "avatar_url": "mxc://example.org/abc123"
+}
+```
+
+## Alternatives
+
+We could define a whole structured system for different thumbnail sizes, though we have a thumbnail
+API which can be used to request whatever size is needed by the client.
+
+## Security considerations
+
+Widget avatars could be non-images. Clients should use the thumbnail API to encourage error responses
+from the server when a widget avatar is a non-image.
+
+## Unstable prefix
+
+While this MSC is not in a released version of the specification, clients should use an alternative
+event type for widgets or use `org.matrix.msc2765.avatar_url` when using `m.widget` or `m.widgets`
+as an event type.