Testing Signup with Apple for free during app development

Hi, I am creating an app where I want to provide the user to signup with apple. Currently it is in developing phase so how can I use signup with apple without any cost associatied . I have gone some docs and all docs was talking about developer program where I need to pay. But for developing phase I want to implement and test in locally for free. so any suggestions.

[Re-Titled by Moderator]

Original Title: signup with apple