initialize IAM as soon as object layer is initialized (#10700)

Allow requests to come in for users as soon as object
layer and config are initialized, this allows users
to be authenticated sooner and would succeed automatically
on servers which are yet to fully initialize.

cmd/gateway-main.go

@@ -300,14 +300,14 @@ func StartGateway(ctx *cli.Context, gw Gateway) {
 	}
 	newObject = NewGatewayLayerWithLocker(newObject)
 
+	// Calls all New() for all sub-systems.
+	newAllSubsystems()
+
 	// Once endpoints are finalized, initialize the new object api in safe mode.
 	globalObjLayerMutex.Lock()
 	globalObjectAPI = newObject
 	globalObjLayerMutex.Unlock()
 
-	// Calls all New() for all sub-systems.
-	newAllSubsystems()
-
 	if gatewayName == NASBackendGateway {
 		buckets, err := newObject.ListBuckets(GlobalContext)
 		if err != nil {
@@ -326,6 +326,8 @@ func StartGateway(ctx *cli.Context, gw Gateway) {
 
 	if enableIAMOps {
 		// Initialize users credentials and policies in background.
+		globalIAMSys.InitStore(newObject)
+
 		go globalIAMSys.Init(GlobalContext, newObject)
 	}