Using Azure AD to authenticate user with React.js (Frontend) and Flash (Backend)

Question

Hi all

My production environment have two apps:

1. React.js (Front-end)
2. Flash (Back-end)

What I wanted to do is:

1. user should be authenticate with MSAL2.0 (Azure AD)
2. Flask API must accept request from React.js

And my proposed method are as below:

1. create 2 Microsoft Azure Web Application Services.
   One for React ; One for Flask
   React on Linux ; Flask on Windows (Different OS)
2. Set up Microsoft Azure AD authentication with React (Front-end)
3. Send the same token ID to Flask after the users authenticate to react successfully.

Here comes with my question:
My proposed method seems still need another authentication between the apps React and Flask. I don't know how I should do this on Azure.

Is there anyone can help and give me more advices?