This mimics xDS's discovery protocol where you must request a resource
explicitly for the exporting side to send those events to you.
As part of this I aligned the overall ResourceURL with the TypeURL that
gets embedded into the encoded protobuf Any construct. The
CheckServiceNodes is now wrapped in a better named "ExportedService"
struct now.
Envoy's SPIFFE certificate validation extension allows for us to
validate against different root certificates depending on the trust
domain of the dialing proxy.
If there are any trust bundles from peers in the config snapshot then we
use the SPIFFE validator as the validation context, rather than the
usual TrustedCA.
The injected validation config includes the local root certificates as
well.
The importing peer will need to know what SNI and SPIFFE name
corresponds to each exported service. Additionally it will need to know
at a high level the protocol in use (L4/L7) to generate the appropriate
connection pool and local metrics.
For replicated connect synthetic entities we edit the `Connect{}` part
of a `NodeService` to have a new section:
{
"PeerMeta": {
"SNI": [
"web.default.default.owt.external.183150d5-1033-3672-c426-c29205a576b8.consul"
],
"SpiffeID": [
"spiffe://183150d5-1033-3672-c426-c29205a576b8.consul/ns/default/dc/dc1/svc/web"
],
"Protocol": "tcp"
}
}
This data is then replicated and saved as-is at the importing side. Both
SNI and SpiffeID are slices for now until I can be sure we don't need
them for how mesh gateways will ultimately work.
