When is authorization needed in a mobile application, and what kind of authorization is needed?

Question

Mobile development

For example, an application for a mini-online store with the ability to order goods, the second option - with the ability to pay for goods. When is authorization required? Is authorization through social networks enough? For a mobile application, do a separate authorization, or authorize somehow using api from the main site? I would be grateful for help.

Answer 1

Authorization is best done at the end of registration.
VK + FB + phone number.
I would do it through the API, but it's more convenient here.