DefaultApplicationInsightsServiceConfigureOptions overwrites user configuration

[ascott18]

• List of NuGet packages and version that you are using: Microsoft.ApplicationInsights.AspNetCore 2.22.0
• Runtime version (e.g. net461, net48, netcoreapp2.1, netcoreapp3.1, etc. You can find this information from the *.csproj file): net8
• Hosting environment (e.g. Azure Web App, App Service on Linux, Windows, Ubuntu, etc.): Windows

Describe the bug

My app has some slightly custom configuration files, as follows:

Program.cs

builder.Configuration
	.AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
	.AddJsonFile("appsettings.localhost.json", optional: true, reloadOnChange: true)
	.AddEnvironmentVariables();

builder.Services.AddApplicationInsightsTelemetry();

appsettings.json (git committed, baseline configuration)

{
  "ApplicationInsights": {
    "ConnectionString": "<Connection string Alpha>"
  },
  // Other stuff
}

appsettings.localhost.json (gitignored, local machine configuration)

{
  "ApplicationInsights": {
    "ConnectionString": "<Connection string Delta>"
  },
  // Other stuff
}

Unfortunately, app insights is ignoring what's in appsettings.localhost.json because after acquiring my own custom configuration, it overlays its own configuration on top of that:

ApplicationInsights-dotnet/NETCORE/src/Microsoft.ApplicationInsights.AspNetCore/Extensions/DefaultApplicationInsightsServiceConfigureOptions.cs

Lines 36 to 43 in e34286b

	if (this.userConfiguration != null)
	{
	configBuilder.AddConfiguration(this.userConfiguration);
	}
	configBuilder.AddJsonFile("appsettings.json", true)
	.AddJsonFile(string.Format(CultureInfo.InvariantCulture, "appsettings.{0}.json", this.hostingEnvironment.EnvironmentName), true)
	.AddEnvironmentVariables();

In my configuration setup, connection string Delta is the last one defined and should therefore "win", but appinsights is re-applying appsettings.json on top of that and therefore Alpha becomes the connection string that gets used.

App insights should not be overriding the user-provided configuration with additional default configuration files. These defaults should be applied to the internal configuration builder first, and then the userConfiguration should be overlayed on top of that so that user configuration is respected.

To Reproduce

Setup a plain aspnetcore project with the above 3 config files.