I noticed something strange when injecting ITokenAcquisition.
You can find my code to reproduce the issue here: Github Repo
I use the NuGet Microsoft.Identity.Web 2.18.0 to enable MSAL authentication in my ASP.NET Api (.NET 7)

My Program.cs looks like this:

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddMicrosoftIdentityWebApi(builder.Configuration)
    .EnableTokenAcquisitionToCallDownstreamApi()
    .AddInMemoryTokenCaches();

// Add services to the container.

builder.Services.AddControllers();
builder.Services.AddHostedService<QueuedHostedService>();
var app = builder.Build();

// Configure the HTTP request pipeline.

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();

You can see that together with my API, a background service is also running:

public class QueuedHostedService : BackgroundService
{
    ITokenAcquisition _tokenAcquisition;
    public QueuedHostedService(ITokenAcquisition tokenAcquisition)
    {
        _tokenAcquisition = tokenAcquisition;
    }


    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        await BackgroundProcessing(stoppingToken);
    }

    private async Task BackgroundProcessing(CancellationToken stoppingToken)
    {
        var token = await _tokenAcquisition.GetAccessTokenForAppAsync("api://0f5ff0f2-5a7f-430e-8ea1-6e133055990e/.default");
        while (!stoppingToken.IsCancellationRequested)
        {
            Console.WriteLine("Executing...");
        }
    }

    public override async Task StopAsync(CancellationToken stoppingToken)
    {
        // "Queued Hosted Service is stopping.");

        await base.StopAsync(stoppingToken);
    }
}

This service uses ITokenAcquisition to get an access token for another API (could be the graph or so)

My controller action looks almost standard, but has the Authorize-Attribute

[Authorize]
[ApiController]
[Route("[controller]")]
public class WeatherForecastController : ControllerBase
{
    ITokenAcquisition _tokenAcquisition;
    public WeatherForecastController(ITokenAcquisition tokenAcquisition) 
    { 
        _tokenAcquisition = tokenAcquisition;
    }

    private static readonly string[] Summaries = new[]
    {
        "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
    };

    [HttpGet]
    public async Task<IEnumerable<WeatherForecast>> GetAsync()
    {
        var token = await _tokenAcquisition.GetAccessTokenForAppAsync("api://0f5ff0f2-5a7f-430e-8ea1-6e133055990e/.default");
        return Enumerable.Range(1, 5).Select(index => new WeatherForecast
        {
            Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
            TemperatureC = Random.Shared.Next(-20, 55),
            Summary = Summaries[Random.Shared.Next(Summaries.Length)]
        })
        .ToArray();
    }
}

My code works and the background service receives the access token, but only when the ASPNETCORE_ENVIRONMENT variable is set to “Test” or “Production”.

In Development my service fails with the following error message:

Cannot consume scoped service
‘Microsoft.Identity.Web.ITokenAcquisition’ from singleton
‘Microsoft.Extensions.Hosting.IHostedService’.)’

Anybody knows:

• Is it allowed to inject ITokenAcquisition in a background service?
• How can it be that it works in Test or Production modes, but never in Development mode?