Introduces two new public gRPC endpoints (`Login` and `Logout`) and
includes refactoring of the equivalent net/rpc endpoints to enable the
majority of logic to be reused (i.e. by extracting the `Binder` and
`TokenWriter` types).
This contains the OSS portions of the following enterprise commits:
- 75fcdbfcfa6af21d7128cb2544829ead0b1df603
- bce14b714151af74a7f0110843d640204082630a
- cc508b70fbf58eda144d9af3d71bd0f483985893
Cross port of ent #1383 "Reject non-default datacenter when making partitioned ACLs"
On the OSS side this is a minor refactor to add some more checks that are only applicable to enterprise code.
Signed-off-by: Mark Anderson <manderson@hashicorp.com>
