MSC3991: Power level up! Taking the room to new heights

proposals/3991-increase-power-level.md

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+# MSC3991: Power level up! Taking the room to new heights
+
+Once a room is created, the highest power level is set in stone. Even if you're the only
+admin in the room, if you try to raise your own power level above the initial `100`, it
+just throws a `403 Forbidden` error:
+
+`PUT /_matrix/client/r0/rooms/{roomId}/state/m.room.power_levels` -> `403 Forbidden`
+```json
+{
+    "errcode": "M_FORBIDDEN",
+    "error": "You don't have permission to add ops level greater than your own"
+}
+```
+
+This is dictated by the [authorization rules (auth
+rules)](https://spec.matrix.org/v1.5/rooms/v10/#authorization-rules) around
+`m.room.power_levels` in a room:
+
+>  9. If type is `m.room.power_levels`:
+>     [...]
+> 
+>      8. For each entry being changed in, or removed from, the `users` property, other than the `sender`’s own entry:
+>          1. If the current value is greater than or equal to the `sender`’s current power level, reject.
+>      9. For each entry being added to, or changed in, the `users` property:
+>          1. If the new value is greater than the `sender`’s current power level, reject.
+
+It's possible to have power levels greater than the default `100` (Admin) power level
+but this has to be specified at the time of room creation.
+
+Not being able to adjust the max power level of `users` after the fact means that any
+mistake is baked into the room forever and requires a room upgrade to rectify the
+situation. Sometimes, more flexibility is needed in the power level ranges and this only
+becomes obvious with hindsight.
+
+For example with the [Gitter
+migration](https://blog.gitter.im/2023/02/13/gitter-has-fully-migrated-to-matrix/), we
+synced all Gitter room admins over as users with a power level of `90` and set the power
+level to do any action at `90` so the bridge bot user could maintain a higher power
+level than the rest of the users while giving the room admins autonomy over everything.
+Then later after the migration, we wanted to clean up the power levels and grant room
+admins the true `100` power level to avoid clients labeling `90` as a "Moderator"
+instead of "Admin". But discovered this was impossible to get right because we couldn't
+raise the power level of the bridge bot above `100` to still maintain a higher power
+level. This condundrum is tracked by https://gitlab.com/gitterHQ/gitter.im/-/issues/4
+
+Something like [MSC3915: Owner power
+level](https://github.com/matrix-org/matrix-spec-proposals/pull/3915) could help in a
+situation like this to formalize the position of owner but doesn't help with the
+flexibility of an existing room. For example, imagine this MSC lands before MSC3915, it
+would be nice to just upgrade your room power levels to reflect the new owners role. And
+going beyond MSC3915, it can be useful to set a user/bot above `150` at a later date.
+Imagine wanting a central company bot to maintain control of every room at power level
+`200`. It would be nice to just update your room power levels to achieve this than have
+to upgrade every room.
+
+
+
+## Proposal
+
+This MSC proposes updating the room event auth rules to allow for raising the `sender`'s
+own `users` power level above the current max power level as long as you update all
+others at the same level to the new max level.
+
+This means that if you're a solo admin in the room, you can arbitrarily raise your own
+power level however you want.
+
+If there are multiple admins in the room, then you must raise all other admins to the
+new max power level.
+
+Propsed new auth rule language:
+
+>  9. If type is `m.room.power_levels`:
+>     [...]
+> 
+>      8. For each entry being removed from the `users` property, other than the `sender`’s own entry:
+>          1. If the current value is greater than or equal to the `sender`’s current power level, reject.
+>      9. For each entry being added to, or changed in, the `users` property:
+>          1. If the new value is greater than the `sender`’s current power level and the `sender` *doesn't have* the highest power level in the room, reject.
+>          1. If the new value is greater than the `sender`’s current power level, the `sender` *has* the highest power level in the room, but doesn't raise everyone else with the current highest power level to the new value, reject.
+
+Because this MSC changes the authorization rules of a room, it requires a new room
+version to ensure all participating servers are authorizing events and state
+consistently.
+
+
+## Potential issues
+
+*None surmised so far*
+
+
+## Alternatives
+
+Room upgrades allow for creating a new room where you can initially specify
+`m.room.power_levels` as desired. There is nothing restricting the integer range that
+`users` field of `m.room.power_levels` so all of the same end results can be achieved
+this way. This has all of the flexibility downsides mentioned for existing rooms in the
+intro/context paragraphs above though.
+
+
+## Security considerations
+
+Changes to auth rules requires careful consideration of how things interact and the
+language should be explicit in what's allowed/rejected. Please review the proposed
+changes for holes in the logic.
+
+
+## Unstable room version
+
+While this feature is in development, the proposed behavior can be trialed with the
+`org.matrix.msc3991` unstable room version and `org.matrix.msc3991v2`, etc as we develop
+and iterate along the way.