Exam SC-100 topic 3 question 27 discussion

A customer uses Azure to develop a mobile app that will be consumed by external users as shown in the following exhibit.

You need to design an identity strategy for the app. The solution must meet the following requirements:
✑ Enable the usage of external IDs such as Google, Facebook, and Microsoft accounts.
✑ Use a customer identity store.
✑ Support fully customizable branding for the app.
Which service should you recommend to complete the design?