core/identity: refactor identity manager (#5091)

* core/identity: add data store for thread-safe storage of sessions and users

* wip

* add test

* wip

* clean up context

* fix nil session error

* add stop message

* remove log

* use origin context

* use base context for manager calls

* use manager context for syncers too

* add runtime flag

* rename legacy lease

* add comment

* use NotSame

* add comment

* Update internal/identity/manager/manager.go

Co-authored-by: Kenneth Jenkins <51246568+kenjenkins@users.noreply.github.com>

* lint

---------

Co-authored-by: Kenneth Jenkins <51246568+kenjenkins@users.noreply.github.com>

internal/identity/legacymanager/sync.go

@@ -0,0 +1,55 @@
+package legacymanager
+
+import (
+	"context"
+
+	"github.com/pomerium/pomerium/internal/atomicutil"
+	"github.com/pomerium/pomerium/pkg/grpc/databroker"
+)
+
+type dataBrokerSyncer struct {
+	cfg *atomicutil.Value[*config]
+
+	update chan<- updateRecordsMessage
+	clear  chan<- struct{}
+
+	syncer *databroker.Syncer
+}
+
+func newDataBrokerSyncer(
+	_ context.Context,
+	cfg *atomicutil.Value[*config],
+	update chan<- updateRecordsMessage,
+	clear chan<- struct{},
+) *dataBrokerSyncer {
+	syncer := &dataBrokerSyncer{
+		cfg: cfg,
+
+		update: update,
+		clear:  clear,
+	}
+	syncer.syncer = databroker.NewSyncer("identity_manager", syncer)
+	return syncer
+}
+
+func (syncer *dataBrokerSyncer) Run(ctx context.Context) (err error) {
+	return syncer.syncer.Run(ctx)
+}
+
+func (syncer *dataBrokerSyncer) ClearRecords(ctx context.Context) {
+	select {
+	case <-ctx.Done():
+	case syncer.clear <- struct{}{}:
+	}
+}
+
+func (syncer *dataBrokerSyncer) GetDataBrokerServiceClient() databroker.DataBrokerServiceClient {
+	return syncer.cfg.Load().dataBrokerClient
+}
+
+func (syncer *dataBrokerSyncer) UpdateRecords(ctx context.Context, _ uint64, records []*databroker.Record) {
+	select {
+	case <-ctx.Done():
+	case syncer.update <- updateRecordsMessage{records: records}:
+	}
+}