Issue in safari test automation

We are facing issue while automating test cases on Safari browser in mac machine. We following Selenium grid Hub architecture and launching safari browser on Mac machine from window machine using Hub.

It launches browser and enter URL in address bar using apple script which executed using power shell. Then we go for entering credentials using apple script, but it pop up message as, so we cant proceed further

If anyone one have idea regarding above issue, Then please reply asap.