Authorization drivers - follow up

[markylaing]

There are a few non-major comments on #12313 that should be addressed:

• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371456339
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371469637
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371540450
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371473486
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371474461
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371474960
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371475025
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371491615
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371497648
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371503174
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371507083
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371514896
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371517356
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371519767
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371521053
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371526260
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371528374
• [ ] https://github.com/canonical/lxd/pull/12313#discussion_r1371531766