Fluent Configuration validation example in .net 7 and web api

ApiSettings.cs

using System.ComponentModel.DataAnnotations;

namespace DotnetConsoles.Configuration.Api;

public class ApiSettings
{
    [Required, Url, MinLength(10), ]
    public string WebhookUrl { get; set; } = null!;

    [Required, MinLength(3)]
    public string DisplayName { get; set; } = null!;

    public bool Enabled { get; set; }

    [Required]
    public SubSettings SubSettings { get; set; } = null!;
}

public class SubSettings
{
    [Required]
    public string CoolName { get; set; } = null!;
}

ApiSettingsValidator.cs

using FluentValidation;

namespace DotnetConsoles.Configuration.Api.Validation;

public class ApiSettingsValidator : AbstractValidator<ApiSettings>
{
    public ApiSettingsValidator()
    {
        RuleFor(setting => setting.WebhookUrl)
            .NotNull().NotEmpty()
            .MinimumLength(10)
            .Must(StringMustBeUri);

        RuleFor(setting => setting.DisplayName)
            .NotNull().NotEmpty()
            .MinimumLength(3);

        RuleFor(setting => setting.SubSettings)
            .NotNull().NotEmpty();
    }

    private static bool StringMustBeUri(string arg)
    {
        return Uri.TryCreate(arg, UriKind.Absolute, out var resultUri)
            && resultUri.Scheme == Uri.UriSchemeHttps;
    }
}

Configuration.Api.csproj

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net7.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="FluentValidation" Version="11.4.0" />
    <PackageReference Include="Microsoft.Extensions.Options" Version="7.0.0" />
    <PackageReference Include="Swashbuckle.AspNetCore" Version="6.4.0" />
  </ItemGroup>

</Project>

ConfigurationExtensions.cs

using DotnetConsoles.Configuration.Api.Validation;

namespace DotnetConsoles.Configuration.Api.Extensions;

public static class ConfigurationExtensions
{
    public static WebApplicationBuilder ConfigurationSetup(this WebApplicationBuilder builder)
    {
        // Configuration setup
        builder.Configuration
            .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
            .AddJsonFile($"appsettings.{builder.Environment.EnvironmentName}.json", true, true);

        // Validate configuration on startup
        builder.Services.AddOptions<ApiSettings>()
            .BindConfiguration(nameof(ApiSettings))
            .ValidateDataAnnotations()
            .Validate(v =>
                v.WebhookUrl.StartsWith("https://"),
                $"{nameof(ApiSettings.WebhookUrl)} must start with https://")
            .ValidateOnStart();

        // Fluent validation alternative
        builder.Services.AddOptions<ApiSettings>()
            .BindConfiguration(nameof(ApiSettings))
            .Validate(v =>
            {
                var validator = new ApiSettingsValidator();
                return validator.Validate(v).IsValid;
            })
            .ValidateOnStart();

        return builder;
    }
}

Program.cs

using DotnetConsoles.Configuration.Api.Endpoints;
using DotnetConsoles.Configuration.Api.Extensions;

var builder = WebApplication.CreateBuilder(args);

// Load and setup configurations
builder.ConfigurationSetup();

// Security settings
app.UseHttpsRedirection();

app.Run();