tokend is responsible for issuing service-scoped tokens based on the token held
and generated by the Vault Agent.
It can also generate "server-user" scoped tokens, which exist for convenience's
sake: they are not a strong attestation of the user on the machine, and have
limited privileges compared to a Vault token issued using e.g. `vault login
-method=oidc`.
I want to be able to rescope these policies down in tokend, which means that I
can't have policies attached to the server's *identity*. Instead, we put these
on the approle instead, which allows us to down-scope all of these.
