[teams 4/5] SQL authorization

[kim]

Permissions for evaluating SQL/DML are not generally "actions", but more a set of permissions that are checked during evaluation.

To make this work with the teams feature, this patch extends AuthCtx to allow checking a set of permissions as mandated by the spec. This set is a bit more fine-grained than "is owner", so as to avoid baking in the concept of teams/collaborators, or assumptions about what a role might entail. Both are likely to evolve in the future, so evaluation of permissions / capabilities should be confined to the impl of the Authorization trait.

Unlike "actions", the AuthCtx must be able to evaluate permission checks quickly and without side-effects, nor can it enter an async context. In that sense, it is precomputed (if you will), and stored as a closure in the AuthCtx for external authorization.

A challenge posed is how to thread through the constructed AuthCtx for subscriptions.

A tempting approach would have been to equip the HostController with the ability to summon an AuthCtx. That, however, would have created a gnarly circular dependency, because the HostController also controls the controldb, which itself demands an AuthCtx.

Instead, the AuthCtx is obtained in the endpoint handler and passed to each method call that requires one. That's less pretty, but more effective.