add ability to specify user for rkt

CHANGELOG.md

@@ -26,6 +26,7 @@ IMPROVEMENTS:
  * driver/docker: Adds support for `ulimit` and `sysctl` options [GH-3568]
  * driver/docker: Adds support for StopTimeout (set to the same value as
    kill_timeout [GH-3601]
+ * driver/rkt: Add support for passing through user [GH-3612]
  * driver/qemu: Support graceful shutdowns on unix platforms [GH-3411]
  * template: Updated to consul template 0.19.4 [GH-3543]
  * core/enterprise: Return 501 status code in Nomad Pro for Premium end points

client/driver/rkt.go

@@ -569,6 +569,11 @@ func (d *RktDriver) Start(ctx *ExecContext, task *structs.Task) (*StartResponse,
 
 	}
 
+	// If a user has been specified for the task, pass it through to the user
+	if task.User != "" {
+		prepareArgs = append(prepareArgs, fmt.Sprintf("--user=%s", task.User))
+	}
+
 	// Add user passed arguments.
 	if len(driverConfig.Args) != 0 {
 		parsed := ctx.TaskEnv.ParseAndReplace(driverConfig.Args)