Call back-end API with a JWT access token

[TonyTroeff]

Hello, guys!
I have the following setup:

• A back-end API (written in ASP.Net Core) that authenticates users via a JWT token generated by Azure B2C.
• A client front-end app (written in Next.js) that authenticates users via Azure B2C.

The question I have is how am I supposed to retrieve a plain authentication token that I can pass to my back-end API so the authenticated users in the client app can be authenticated in the back-end as well?