Authenticating ASP.NET Core Background Service to Azure/Office365 through an Angular SPA using msal-angular

Question

I'm building a web application; the frontend is a SPA using Angular8 and the backend is an ASP.NET Core 3.1 Web API. The application already has its own authentication scheme, setup using JWT Bearer tokens.

Now I need to add the ability for the backend to sync events on the Office365 calendar of the users. The requirements are:

• Users should login to their Microsoft Office365 account on the frontend;
• The frontend should "save" the results of the authentication on the backend, allowing the backend to periodically interact with the Micosoft Graph API.
• In the (rare) case for some reasons the authentication must be renewed (for example different rights/scopes are required), the backend will notify the frontend that a new login is required.

I am currently able to perform a successful login in example applications using MSAL.NET and msal-angular, but what I cannot do is to pass the result of the authentication I get from msal-angular to .NET and use it to proceed with further calls and token renewals.

I am thinking about modifying/extending the msal-angular library to support the MSALv3 cache serialization scheme used in MSAL.NET and sending the cache to my web app, but it seem a very complicated and fragile (I see the internals of those libs are not stable across versions).

So, is this use case supported in some other way by MSAL? Should I use some different libraries?

Answer 1

You can go through the following docs to see if they are helpful in your scenario.

1. Acquire and cache tokens using the Microsoft Authentication Library (MSAL).
2. Single-page application: Acquire a token to call an API
3. Get a token from the token cache using MSAL.NET
4. Initialize client applications using MSAL.NET