Hi!
Not sure if I misunderstood. But, if you have that Secret stored (similar to my previous screenshot) and User A logs in with B2C, the Secret B2C Access Token is set to automatically upon login. This secret can hold 1 value for each user, so if user B logs in the same time, value is different for user B.
For authenticating towards some resource in Azure using the (personal) access token: Use the Web Request with “Bearer” authentication towards the resource that the user have access to, and select the secret B2C Access Token as Bearer Token. When User A executes the web request, then User A’s access token is used. And similar for User B.