MSC4441: User Profile Annotations ("Profile Notes")

proposals/4441-user-profile-annotations.md

@@ -0,0 +1,93 @@
+# MSC4441: User Profile Annotations ("Profile Notes")
+
+Many platforms, such as Discord, provide a capability for a user to leave personal "notes" on a user's profile. Matrix,
+however, has no similar functionality that can be shared between different clients. This proposal builds User Profile
+Annotations, a method for storing encrypted, private metadata on user profiles.
+
+Because profile annotations may contain sensitive information about the users they reference, the data is made
+optionally encryptable using [MSC4483: Encrypted Account Data][MSC4483].
+
+## Proposal
+
+This proposal introduces a new `m.profile_annotations` Account Data entry, allowing the storage of free text (and other
+future annotations) on users. The framework introduced within this MSC provides room for future extension into other
+forms of user context, such as contact labels and custom nickname overrides.
+
+### `m.profile_annotations`
+
+A new [encryptable account data][] value, `m.profile_annotations`, is stored in [`account_data`][]. The `content` MUST
+be a mapping between valid user MXIDs and annotations stored on that user. Within a user, the `m.text` property
+represents a textual annotation ("note") on that user, with the object holding an ordered array as defined by [MSC1767][].
+
+`m.profile_annotations`:
+
+```json
+{
+    "@logn:zirco.dev": {
+        "m.text": [
+            { "body": "<i>Hello world</i>", "mimetype": "text/html" },
+            { "body": "Hello world" }
+        ]
+    }
+}
+```
+
+As `m.profile_annotations` is encryptable, it may be optionally encrypted with the format specified within [MSC4483][].
+
+`m.profile_annotations`:
+
+```json
+{
+    "encrypted": {
+        "iv": "...",
+        "ciphertext": "...",
+        "mac": "..."
+    }
+}
+```
+
+## Potential issues
+
+#### Concurrent writes
+Account data is last-write-wins. The usage of one account data entry representing all users may lead to a data race in
+rare scenarios (although this tradeoff was accepted to keep the behavior similar to existing state like `m.direct`).
+
+#### Clients that lack support for Encrypted Account Data
+
+If clients lack support for Encrypted Account Data, an edit to one singular entry will risk overwriting all other
+profile annotations.
+
+## Alternatives
+
+#### Store annotations as a new API endpoint
+Rather than using `account_data`, a new dedicated endpoint for annotations would be created. Rejected because it
+requires substantial serverside changes, this MSC aims to be entirely clintside.
+
+## Trust and Safety considerations
+
+Profile annotations are the property of one singular user and are never shared with others by the server. Still, a
+server does not gain any moderation visibility into the content potentially being hosted and accessible to their users.
+Because the content is scoped to only a singular user, this is acceptable.
+
+## Future extensibility
+
+In the future, this MSC may be built on to implement nickname or avatar overrides, general user tagging functionalities,
+etc.
+
+## Unstable prefix
+
+Before this MSC is accepted, implementations should use the unstable `account_data` events:
+
+| Stable identifier        | Purpose                                  | Unstable identifier                      |
+| ------------------------ | ---------------------------------------- | ---------------------------------------- |
+| `m.profile_annotations`  | Storage of User Profile Annotations      | `dev.zirco.msc4441.profile_annotations`  |
+
+## Dependencies
+
+This MSC depends on the following proposals not yet accepted:
+* [MSC4483: Encrypted Account Data][MSC4483]
+
+[MSC1767]: https://github.com/matrix-org/matrix-spec-proposals/pull/1767
+[MSC4483]: https://github.com/matrix-org/matrix-spec-proposals/pull/4483
+[`account_data`]: https://spec.matrix.org/v1.18/client-server-api/#client-config
+[encryptable account data]: https://github.com/thetayloredman/matrix-spec-proposals/blob/encrypted-account-data/proposals/4483-encrypted-account-data.md#encrypted-account-data