https://github.com/linkerd/linkerd2/pull/2521 introduces an "Identity"
controller, but there is no way to include it in linkerd installation.
This change alters the `install` flow as follows:
- An Identity service is _always_ installed;
- Issuer credentials may be specified via the CLI;
- If no Issuer credentials are provided, they are generated each time `install` is called.
- Proxies are NOT configured to use the identity service.
- It's possible to override the credential generation logic---especially
for tests---via install options that can be configured via the CLI.
This change introduces a new Identity service implementation for the
`io.linkerd.proxy.identity.Identity` gRPC service.
The `pkg/identity` contains a core, abstract implementation of the service
(generic over both the CA and (Kubernetes) Validator interfaces).
`controller/identity` includes a concrete implementation that uses the
Kubernetes TokenReview API to validate serviceaccount tokens when
issuing certificates.
This change does **NOT** alter installation or runtime to include the
identity service. This will be included in a follow-up.
Oliver Gould