Requests without an ACL token that pass thru the client's HTTP API are treated
as though they come from the client itself. This allows bypass of ACLs on RPC
requests where ACL permissions are checked (like `Job.Register`). Invalid tokens
are correctly rejected.
Fix the bypass by only setting a client ID on the identity if we have a valid node secret.
Note that this changeset will break rate metrics for RPCs sent by clients
without a client secret such as `Node.GetClientAllocs`; these requests will be
recorded as anonymous.
Future work should:
* Ensure the node secret is sent with all client-driven RPCs except
`Node.Register` which is TOFU.
* Create a new `acl.ACL` object from client requests so that we
can enforce ACLs for all endpoints in a uniform way that's less error-prone.~
Tim Gross