send and receive Private through ReadResource

Send Private data blob through ReadResource as well. This will allow for
extra flexibility for future providers that may want to pass data out of
band through to their resource Read functions.

helper/plugin/grpc_provider.go

@@ -535,6 +535,11 @@ func (s *GRPCProviderServer) ReadResource(_ context.Context, req *proto.ReadReso
 		Msgpack: newStateMP,
 	}
 
+	// helper/schema did previously handle private data during refresh, but
+	// core is now going to expect this to be maintained in order to
+	// persist it in the state.
+	resp.Private = req.Private
+
 	return resp, nil
 }
 

plugin/grpc_provider.go

@@ -330,6 +330,7 @@ func (p *GRPCProvider) ReadResource(r providers.ReadResourceRequest) (resp provi
 	protoReq := &proto.ReadResource_Request{
 		TypeName:     r.TypeName,
 		CurrentState: &proto.DynamicValue{Msgpack: mp},
+		Private:      r.Private,
 	}
 
 	protoResp, err := p.client.ReadResource(p.ctx, protoReq)
@@ -348,6 +349,7 @@ func (p *GRPCProvider) ReadResource(r providers.ReadResourceRequest) (resp provi
 		}
 	}
 	resp.NewState = state
+	resp.Private = protoResp.Private
 
 	return resp
 }

providers/provider.go

@@ -176,6 +176,10 @@ type ReadResourceRequest struct {
 
 	// PriorState contains the previously saved state value for this resource.
 	PriorState cty.Value
+
+	// Private is an opaque blob that will be stored in state along with the
+	// resource. It is intended only for interpretation by the provider itself.
+	Private []byte
 }
 
 type ReadResourceResponse struct {
@@ -184,6 +188,10 @@ type ReadResourceResponse struct {
 
 	// Diagnostics contains any warnings or errors from the method call.
 	Diagnostics tfdiags.Diagnostics
+
+	// Private is an opaque blob that will be stored in state along with the
+	// resource. It is intended only for interpretation by the provider itself.
+	Private []byte
 }
 
 type PlanResourceChangeRequest struct {

terraform/eval_refresh.go

@@ -55,6 +55,7 @@ func (n *EvalRefresh) Eval(ctx EvalContext) (interface{}, error) {
 	req := providers.ReadResourceRequest{
 		TypeName:   n.Addr.Resource.Type,
 		PriorState: priorVal,
+		Private:    state.Private,
 	}
 
 	provider := *n.Provider
@@ -87,6 +88,7 @@ func (n *EvalRefresh) Eval(ctx EvalContext) (interface{}, error) {
 
 	newState := state.DeepCopy()
 	newState.Value = resp.NewState
+	newState.Private = resp.Private
 
 	// Call post-refresh hook
 	err = ctx.Hook(func(h Hook) (HookAction, error) {