Azure App Configuration variables are not available in startup on ASP.NET

Question

I ran into a problem with retrieving configuration from Azure App Configuration in Startup methods.

public static IConfigurationSection GetAuthSection()
{
    var intermediateConfig = new ConfigurationBuilder().AddJsonFile("appsettings.json", true).Build();
    var appConfiguration = intermediateConfig["AppConfigurationConnectionString"];

    var builder = new ConfigurationBuilder();
    if (!string.IsNullOrWhiteSpace(appConfiguration))
    {
        builder.AddAzureAppConfiguration(opt =>
        {
            opt.Connect(appConfiguration).Select("Tool*");
        });
    }
    
    var configRoot = builder.Build();
    var debugConfig = configRoot.GetDebugView();
    return configRoot.GetSection("Tool:Auth");
}

GetDebugView method returns such string that is OK for me.

Tool:
  Auth:
    CallbackPath=***
    ClientId=***
    ClientSecret=***
    Instance=***
    Scopes=***
    SignedOutCallbackPath=***
    TenantId=***

But method GetSection returns null in Value property.

Method GetAuthSection is used in Startup.cs in method ConfigureServices:

public void ConfigureServices(IServiceCollection services)
{ 
    services.AddAuthentication(OpenIdConnectDefaults.AuthenticationScheme)
        .AddMicrosoftIdentityWebApp(ConfigurationLoader.GetAuthSection());
    
    ...
}

I can't hold Auth data in the local config due to some reasons. After the server is built and it is running these data can be retrieved from the configuration.

Answer 1

Need to use method AddEnvironmentVariables to transfer data from AzureAppConfigurationProvider to IConfiguration