Access Azure Application Settings using IConfiguration

I have a setting in my Application settings on my Azure Web App set up like so:

I'm trying to access it in the code like so: configuration["AppSettings:LASTFM_API_KEY"]

This works when I have the secret set up in my secrets.json file like so:

But not when I publish my app to Azure. I first tried it in Azure as LASTFM_API_KEY and then tried adding AppSettings__, neither worked.

How can I access this secret when I publish my app? Is it possible to access it using configuration in the same way both locally and when published to Azure?

I was missing the AddEnvironmentVariables() call, and also this needs to be called after any calls that might overwrite the value with a similar value in another file (like appsettings.json). I put it last like so:

IConfiguration configuration = new ConfigurationBuilder()
    .AddJsonFile("appsettings.json")
    .AddUserSecrets(Assembly.GetEntryAssembly()!, true)
    .AddEnvironmentVariables()
    .Build();