Log authorized username

This is useful to know which user pulled/pushed which repo.

Signed-off-by: Manish Tomar <manish.tomar@docker.com>

registry/handlers/app.go

@@ -862,7 +862,7 @@ func (app *App) authorized(w http.ResponseWriter, r *http.Request, context *Cont
 		return err
 	}
-	dcontext.GetLogger(ctx).Info("authorized request")
+	dcontext.GetLogger(ctx, auth.UserNameKey).Info("authorized request")
 	// TODO(stevvooe): This pattern needs to be cleaned up a bit. One context
 	// should be replaced by another, rather than replacing the context on a
 	// mutable object.