This change reintroduces identity hinting to the destination service.
The Get endpoint includes identities for pods that are injected with an
identity-mode of "default" and have the same linkerd control plane.
A `serviceaccount` label is now also added to destination response
metadata so that it's accessible in prometheus and tap.
This change adds a new `linkerd2-proxy-identity` binary to the `proxy`
container image as well as a `linkerd2-proxy-run` entrypoint script.
The inject process now sets environment variables on pods to support
identity, including identity names for the destination and identity
services.
As the proxy starts, the identity helper creates a key and CSR in a
tmpfs. As the proxy starts, it reads these files, as well as a
serviceaccount token, and provisions a certificate from controller.
The proxy's /ready endpoint will not succeed until a certificate has
been provisioned.
The proxy will not participate in identity with services other than the
controllers until the Destination controller is modified to provide
identities via discovery.
Oliver Gould