1. Configuration Providers

.NET Core supports many configuration sources.

var builder = WebApplication.CreateBuilder(args);

builder.Configuration
    .AddJsonFile("appsettings.json")
    .AddJsonFile(
        $"appsettings.{builder.Environment.EnvironmentName}.json",
        optional: true
    )
    .AddEnvironmentVariables()
    .AddCommandLine(args);

2. Strongly Typed Configuration

Map configuration to C# classes using the IOptions pattern.

// appsettings.json
{
  "MySettings": {
    "SiteTitle": "My App",
    "MaxItems": 10
  }
}

public class MySettings
{
    public string SiteTitle { get; set; }
    public int MaxItems { get; set; }
}
builder.Services.Configure<MySettings>(
    builder.Configuration.GetSection("MySettings")
);

public class HomeController : Controller
{
    private readonly MySettings _settings;
    public HomeController(IOptions<MySettings> options)
    {
        _settings = options.Value;
    }
}

3. Validate Options at Startup

builder.Services
    .AddOptions<MySettings>()
    .Bind(builder.Configuration.GetSection("MySettings"))
    .Validate(settings => settings.MaxItems > 0, "MaxItems must be > 0");

4. Reloading Config on Changes

Enable hot reload for appsettings.json.

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

Use IOptionsSnapshot<T> to get updated config per request.

5. Secret Management

Use User Secrets for local development.

dotnet user-secrets init
dotnet user-secrets set "MySettings:ApiKey" "123456"

builder.Configuration
       .AddUserSecrets<Program>();

6. Azure Key Vault Integration

builder.Configuration.AddAzureKeyVault(
    new Uri("https://yourvault.vault.azure.net/"),
    new DefaultAzureCredential());

Make sure your app is registered and granted access to the vault.

7. Custom Configuration Provider

You can create a custom provider for things like databases or external services.

Points to consider