MSC3391: API to delete account data

proposals/3391-account-data-delete.md

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+# MSC3391: Deleting account data
+
+## Proposal
+
+### Endpoints
+
+Account data and room data currently have the following endpoints;
+
+```
+GET /_matrix/client/r0/user/{userId}/account_data/{type}
+
+PUT /_matrix/client/r0/user/{userId}/account_data/{type}
+
+GET /_matrix/client/r0/user/{userId}/rooms/{roomId}/account_data/{type}
+
+PUT /_matrix/client/r0/user/{userId}/rooms/{roomId}/account_data/{type}
+```
+
+This proposal aims to add the following two endpoints;
+
+```
+DELETE /_matrix/client/r0/user/{userId}/account_data/{type}
+
+DELETE /_matrix/client/r0/user/{userId}/rooms/{roomId}/account_data/{type}
+```
+
+With no body.
+
+### Sync
+
+Account Data changes are announced through sync, this proposal also aims to add the following to sync;
+
+```json5
+
+{
+  // ...
+  "account_data_removed": ["m.direct", "m.push_rules"], // <- NEW
+  // ...
+  "rooms": {
+    "join": {
+      "!this-is-a-room:example.com": {
+        // ...
+        "account_data_removed": ["m.tag", "m.fully_read"], // <- NEW
+        // ...
+      }
+    }
+  },
+  // ...
+}
+
+```
+
+Which are the tags that were removed since `since` and `next_batch`, if `since` is specified and valid.
+
+
+## Potential issues
+
+Desync is possible, and so if there's a situation where the client has a different view on account
+data than the server, it should query the account data wherever possible.
+
+## Security considerations
+
+No considerable security problems, other than the fact that a user can potentially delete important data.
+
+Though, for the purposes of this proposal, that is seen as a proper feature of CRUD :)
+
+## Unstable prefix
+
+When implementing this proposal, servers should use the `org.matrix.msc3391` unstable prefix;
+
+```
+DELETE /_matrix/client/unstable/org.matrix.msc3391/user/{userId}/account_data/{type}
+
+DELETE /_matrix/client/unstable/org.matrix.msc3391/user/{userId}/rooms/{roomId}/account_data/{type}
+```
+
+And `org.matrix.msc3391.account_data_removed` for sync.
+
+**Note:** As this operation would be largely "unknown" to clients,
+cache invalidation problems could occur as clients could aggressively cache account data.