Microsoft.Identity.Web inside an Azure function

Question

I need to call a downstream API, i.e., PowerBI Service, from inside my Azure Function. I have a working example inside a web app but I am not able to make it happen inside my Azure Function.

In the web app sample, the configuration happens via Microsoft.Identity.Web like this.

services.AddMicrosoftIdentityWebAppAuthentication(Configuration)
                    .EnableTokenAcquisitionToCallDownstreamApi()
                    .AddInMemoryTokenCaches();

Then inside a controller I am able to receive a ITokenAcquisition object injected in the constructor

public HomeController(ITokenAcquisition tokenAcquisition, ...
{
    this._tokenAcquisition = tokenAcquisition;

and I can do:

var accessToken = 
    this._tokenAcquisition.GetAccessTokenForAppAsync(powerbiApiDefaultScope).Result;

and get a token credential like this:

var tokenCredentials = new TokenCredentials(accessToken, "Bearer");

With this tokenCredentials I can achieve my goal, i.e., instantiate a PowerBIClient class to interact with PowerBI service.

var client = new PowerBIClient(new Uri(urlPowerBiServiceApiRoot), tokenCredentials);

The problem is that I am not able to set the configuration in the Startup class of my isolated Azure Function. Therefore, I cannot get a ITokenAcquisition injected in my Azure Fucntion that allows me to get an access token.

Could anybody please advice? Thanks a million.