Proposal to support widget avatars

proposals/0000-widget-avatars.md

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+# MSC0000: 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
+
+In the widget's `data`, a new optional paramater named `avatar_url` is added. 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.
+
+## 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
+
+Not applicable - this is backwards compatible with specification and an allowed property of `data`
+without this MSC.