Minimal APIのミドルウェアとフィルター

ミドルウェアとエンドポイントフィルターの違い

Minimal APIs へのミドルウェアの追加

var app = builder.Build();

app.UseHttpsRedirection();
app.UseAuthentication();
app.UseAuthorization();
app.UseRateLimiter();

app.MapGet("/secure", () => "Protected endpoint")
   .RequireAuthorization();

app.Run();

インラインエンドポイントフィルター

app.MapGet("/guarded", () => "Secret data")
   .AddEndpointFilter(async (ctx, next) =>
   {
       var header = ctx.HttpContext.Request.Headers["X-Api-Key"];
       if (header != "my-secret-key")
           return Results.Unauthorized();

       return await next(ctx); // proceed to handler
   });

クラスベースのエンドポイントフィルター

public class LoggingFilter : IEndpointFilter
{
    private readonly ILogger<LoggingFilter> _logger;
    public LoggingFilter(ILogger<LoggingFilter> logger) => _logger = logger;

    public async ValueTask<object?> InvokeAsync(
        EndpointFilterInvocationContext ctx,
        EndpointFilterDelegate next)
    {
        _logger.LogInformation("Before: {Path}", ctx.HttpContext.Request.Path);
        var result = await next(ctx);
        _logger.LogInformation("After: {Path}",  ctx.HttpContext.Request.Path);
        return result;
    }
}

// Apply to a group
app.MapGroup("/api").AddEndpointFilter<LoggingFilter>();

例外処理ミドルウェア

builder.Services.AddProblemDetails();

var app = builder.Build();

app.UseExceptionHandler();
// OR for custom logic:
app.UseExceptionHandler(errApp =>
    errApp.Run(async ctx =>
    {
        var ex = ctx.Features.Get<IExceptionHandlerFeature>()?.Error;
        ctx.Response.StatusCode = 500;
        await ctx.Response.WriteAsJsonAsync(new { error = ex?.Message });
    }));

ショートサーキットミドルウェア

// Block known bad bots at the edge
app.MapGet("/robots.txt", () => "User-agent: *\nDisallow: /")
   .ShortCircuit(); // .NET 8: returns response immediately

// Or in a filter:
app.MapGet("/maintenance", () => "OK")
   .AddEndpointFilter((ctx, next) =>
       ValueTask.FromResult<object?>(Results.StatusCode(503)));

.NET 7 以降のレート制限

using System.Threading.RateLimiting;

builder.Services.AddRateLimiter(opt =>
{
    opt.AddFixedWindowLimiter("fixed", o =>
    {
        o.PermitLimit     = 10;
        o.Window          = TimeSpan.FromSeconds(10);
        o.QueueLimit      = 0;
        o.QueueProcessingOrder = QueueProcessingOrder.OldestFirst;
    });
    opt.RejectionStatusCode = StatusCodes.Status429TooManyRequests;
});

app.UseRateLimiter();
app.MapGet("/search", Search).RequireRateLimiting("fixed");

CORS の設定

builder.Services.AddCors(opt =>
    opt.AddPolicy("AllowFrontend", policy =>
        policy.WithOrigins("https://myapp.com")
              .AllowAnyHeader()
              .AllowAnyMethod()));

app.UseCors("AllowFrontend");

// Or per endpoint:
app.MapGet("/public-data", () => "data")
   .RequireCors("AllowFrontend");

出力キャッシュミドルウェア

builder.Services.AddOutputCache();

app.UseOutputCache();

app.MapGet("/products", async (AppDbContext db) =>
    Results.Ok(await db.Products.AsNoTracking().ToListAsync()))
   .CacheOutput(p => p.Expire(TimeSpan.FromMinutes(5)));

フィルターの順序とチェーン

app.MapPost("/orders", CreateOrder)
   .AddEndpointFilter<LoggingFilter>()      // runs first
   .AddEndpointFilter<ValidationFilter>()   // runs second
   .AddEndpointFilter<AuthFilter>()         // runs third
   .RequireAuthorization();                 // JWT checked by middleware

実践：API キーミドルウェア

public class ApiKeyMiddleware
{
    private readonly RequestDelegate _next;
    private readonly string _expectedKey;

    public ApiKeyMiddleware(RequestDelegate next, IConfiguration cfg)
    {
        _next = next;
        _expectedKey = cfg["ApiKey"] ?? throw new Exception("ApiKey not configured");
    }

    public async Task InvokeAsync(HttpContext ctx)
    {
        if (!ctx.Request.Headers.TryGetValue("X-Api-Key", out var key)
            || key != _expectedKey)
        {
            ctx.Response.StatusCode = 401;
            await ctx.Response.WriteAsync("Invalid API key");
            return;
        }
        await _next(ctx);
    }
}

app.UseMiddleware<ApiKeyMiddleware>();

確認問題

まとめ：ミドルウェアとフィルター