With generative AI's explosive growth, developers are no longer constrained to static business logic. The ability to build, summarize, explain, and even dynamically generate code or SQL queries has been added to applications. Generative AI APIs (such as Hugging Face, Azure OpenAI, or OpenAI) with.NET 8 can be combined to create intelligent microservices that can generate and comprehend natural language. Learn how to create a microservice driven by generative AI in this tutorial by utilizing the OpenAI GPT API and.NET 8 Minimal APIs.

Step 1. Create a New .NET 8 Web API Project
In your terminal or command prompt:
dotnet new webapi -n GenerativeAIMicroservice
cd GenerativeAIMicroservice

Step 2. Clean Up the Template
Remove default controllers and WeatherForecast examples.
We’ll use a Minimal API style for simplicity.

Step 3. Add Dependencies
Install the following NuGet packages:
dotnet add package OpenAI_API
dotnet add package Newtonsoft.Json

These allow communication with the OpenAI GPT API and handle JSON serialization.

Step 4. Create the AI Service
Create a new file: Services/AiService.cs
using OpenAI_API;
using System.Threading.Tasks;

namespace GenerativeAIMicroservice.Services
{
    public class AiService
    {
        private readonly OpenAIAPI _api;

        public AiService(string apiKey)
        {
            _api = new OpenAIAPI(apiKey);
        }

        public async Task<string> GenerateTextAsync(string prompt)
        {
            var result = await _api.Completions.GetCompletion(prompt);
            return result;
        }
    }
}

This service will handle all Generative API communication.

Step 5. Create the Minimal API Endpoint
In your Program.cs file, add:
using GenerativeAIMicroservice.Services;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddSingleton(new AiService("sk-your-openai-api-key"));  // Replace with your key

var app = builder.Build();

app.MapPost("/api/generate", async (AiService aiService, PromptRequest request) =>
{
    if (string.IsNullOrEmpty(request.Prompt))
        return Results.BadRequest("Prompt is required.");

    var response = await aiService.GenerateTextAsync(request.Prompt);
    return Results.Ok(new { Output = response });
});

app.Run();

record PromptRequest(string Prompt);

Example Request
You can now test your Generative API microservice using Postman or curl.
POST Request

URL:
https://localhost:5001/api/generate

Body (JSON):
{"Prompt": "Write a C# function to reverse a string"}

Example Response
{"Output": "public string ReverseString(string s) { char[] arr = s.ToCharArray(); Array.Reverse(arr); return new string(arr); }"}

Step 6. Containerize with Docker (Optional)
To make it cloud-ready, create a Dockerfile:
FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS base
WORKDIR /app

FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
WORKDIR /src
COPY . .
RUN dotnet publish -c Release -o /app/publish

FROM base AS final
WORKDIR /app
COPY --from=build /app/publish .
ENTRYPOINT ["dotnet", "GenerativeAIMicroservice.dll"]

Then run:
docker build -t generative-ai-service .
docker run -p 8080:80 generative-ai-service

Step 7. Real-World Use Cases

Architecture Overview

Client App (UI)
↓
Generative AI Microservice (.NET 8)
↓
OpenAI / Azure OpenAI API
↓
AI-Generated Response

This architecture makes the AI layer modular, secure, and reusable across multiple projects.

Security Considerations
Do not hardcode API keys — use:

dotnet user-secrets set "OpenAIKey" "sk-your-key"

and retrieve it via:

builder.Configuration["OpenAIKey"]

1. Limit tokens and rate of calls
2. Sanitize user inputs before sending to AI API
3. External References

Conclusion
By integrating Generative AI APIs into a .NET 8 microservice, you can bring AI-driven intelligence into any system — whether for content creation, coding automation, or chatbot applications. This architecture is modular, scalable, and ready for enterprise deployment, bridging traditional software engineering with next-generation AI development.

A cutting-edge, cross-platform, open-source framework for creating scalable and high-performance online applications is called ASP.NET Core. Its architecture guarantees that developers can achieve high throughput, low latency, and effective resource usage for everything from microservices to enterprise-grade APIs. In order to optimize performance and scalability in your ASP.NET Core applications, we'll go over important tactics, setting advice, and code samples in this post.

Understanding Performance and Scalability
Before diving into implementation, let’s define two crucial concepts:

• Performance: How fast your application responds to a single request.

(Example: Reducing response time from 300ms to 100ms).

• Scalability: How well your application handles increased load.

(Example: Handling 10,000 concurrent users without crashing).

ASP.NET Core achieves both through efficient memory management, asynchronous programming, dependency injection, caching, and built-in support for distributed systems.

Using Asynchronous Programming
The ASP.NET Core runtime is optimized for asynchronous I/O operations. By using the async and await keywords, you can free up threads to handle more requests concurrently.

Example: Asynchronous Controller Action
[ApiController]
[Route("api/[controller]")]
public class ProductsController : ControllerBase
{
    private readonly IProductService _productService;

    public ProductsController(IProductService productService)
    {
        _productService = productService;
    }

    [HttpGet("{id}")]
    public async Task<IActionResult> GetProductById(int id)
    {
        var product = await _productService.GetProductAsync(id);

        if (product == null)
            return NotFound();

        return Ok(product);
    }
}

By using Task<IActionResult> , the thread doesn’t block while waiting for I/O-bound operations such as database queries or API calls. This dramatically improves scalability under heavy load.

Optimize Middleware Pipeline
Middleware components handle each request sequentially. Keep your middleware lightweight and avoid unnecessary processing.

Example: Custom Lightweight Middleware
public class RequestTimingMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger<RequestTimingMiddleware> _logger;

    public RequestTimingMiddleware(RequestDelegate next, ILogger<RequestTimingMiddleware> logger)
    {
        _next = next;
        _logger = logger;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        var start = DateTime.UtcNow;
        await _next(context);
        var elapsed = DateTime.UtcNow - start;

        _logger.LogInformation($"Request took {elapsed.TotalMilliseconds} ms");
    }
}

// Registration in Program.cs
app.UseMiddleware<RequestTimingMiddleware>();

Tip :
Place lightweight middleware at the top (like routing or compression), and heavy middleware (like authentication) lower in the pipeline.

Enable Response Caching
Caching reduces the need to recompute results or hit the database repeatedly. ASP.NET Core provides a built-in Response Caching Middleware .
Example: Enable Response Caching
// In Program.cs
builder.Services.AddResponseCaching();

var app = builder.Build();
app.UseResponseCaching();

app.MapGet("/time", (HttpContext context) =>
{
    context.Response.GetTypedHeaders().CacheControl =
        new Microsoft.Net.Http.Headers.CacheControlHeaderValue()
        {
            Public = true,
            MaxAge = TimeSpan.FromSeconds(30)
        };

    return DateTime.UtcNow.ToString("T");
});

Now, subsequent requests within 30 seconds will be served from cache — drastically improving performance.

Optimize Data Access with EF Core
Database access is often the main bottleneck. Use Entity Framework Core efficiently by applying:

• AsNoTracking() for read-only queries
• Compiled queries for repeated access
• Connection pooling

Example: Using AsNoTracking()
public async Task<IEnumerable<Product>> GetAllProductsAsync()
{
    return await _context.Products
        .AsNoTracking()  // Improves performance
        .ToListAsync();
}

If you frequently run similar queries, consider compiled queries :
private static readonly Func<AppDbContext, int, Task<Product?>> _getProductById =
    EF.CompileAsyncQuery((AppDbContext context, int id) =>
        context.Products.FirstOrDefault(p => p.Id == id));

public Task<Product?> GetProductAsync(int id) =>
    _getProductById(_context, id);

Use Output Compression
Compressing responses before sending them to the client reduces bandwidth usage and speeds up delivery.

Example: Enable Response Compression
// In Program.cs
builder.Services.AddResponseCompression(options =>
{
    options.EnableForHttps = true;
    options.MimeTypes = new[] { "text/plain", "application/json" };
});

var app = builder.Build();
app.UseResponseCompression();

Now all application/json responses will be automatically GZIP-compressed.

Scaling Out with Load Balancing
Performance tuning is not enough when traffic grows. Scalability often involves distributing load across multiple servers using:

• Horizontal Scaling : Adding more servers
• Load Balancers : NGINX, Azure Front Door, AWS ELB, etc.

In distributed systems, session state and caching should be externalized (e.g., Redis).

Example: Configure Distributed Cache (Redis)
builder.Services.AddStackExchangeRedisCache(options =>
{
    options.Configuration = "localhost:6379";
});

public class CacheService
{
    private readonly IDistributedCache _cache;

    public CacheService(IDistributedCache cache)
    {
        _cache = cache;
    }

    public async Task SetCacheAsync(string key, string value)
    {
        await _cache.SetStringAsync(key, value, new DistributedCacheEntryOptions
        {
            AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(5)
        });
    }

    public Task<string?> GetCacheAsync(string key) => _cache.GetStringAsync(key);
}

This makes your app stateless, which is essential for load balancing.

Configure Kestrel and Hosting for High Throughput
Kestrel, the built-in ASP.NET Core web server, can handle hundreds of thousands of requests per second when configured properly.

Example: Optimize Kestrel Configuration
builder.WebHost.ConfigureKestrel(options =>
{
    options.Limits.MaxConcurrentConnections = 10000;
    options.Limits.MaxConcurrentUpgradedConnections = 1000;
    options.Limits.RequestHeadersTimeout = TimeSpan.FromSeconds(30);
});

Additionally:

• Use reverse proxy servers (like NGINX or IIS) for static file handling and TLS termination.
• Deploy in containerized environments for auto-scaling (e.g., Kubernetes).
• Use Memory and Object Pooling
• To avoid frequent object allocations and garbage collection, ASP.NET Core supports object pooling .

Example: Using ArrayPool<T>
using System.Buffers;

public class BufferService
{
    public void ProcessData()
    {
        var pool = ArrayPool<byte>.Shared;
        var buffer = pool.Rent(1024); // Rent 1KB buffer

        try
        {
            // Use the buffer
        }
        finally
        {
            pool.Return(buffer);
        }
    }
}

This approach minimizes heap allocations and reduces GC pressure — crucial for performance-sensitive applications.

Minimize Startup Time and Memory Footprint

Avoid unnecessary services in Program.cs .

Use AddSingleton instead of AddTransient where appropriate.

Trim dependencies in *.csproj files.

Example: Minimal API Setup
var builder = WebApplication.CreateBuilder(args);

builder.Services.AddSingleton<IProductService, ProductService>();

var app = builder.Build();

app.MapGet("/products", async (IProductService service) =>
    await service.GetAllProductsAsync());

app.Run();

Minimal APIs reduce boilerplate and improve startup performance.

Monitoring and Benchmarking
You can’t improve what you don’t measure. Use tools like:
dotnet-trace and dotnet-counters

Application Insights

BenchmarkDotNet

Example: Using BenchmarkDotNet
[MemoryDiagnoser]
public class PerformanceTests
{
    private readonly ProductService _service = new();

    [Benchmark]
    public async Task FetchProducts()
    {
        await _service.GetAllProductsAsync();
    }
}

Run this benchmark to identify bottlenecks and memory inefficiencies.

Additional Optimization Tips

• Enable HTTP/2 or HTTP/3 for better parallelism.
• Use CDNs for static assets.
• Employ connection pooling for database and HTTP clients.
• Use IHttpClientFactory to prevent socket exhaustion.

builder.Services.AddHttpClient("MyClient")
.SetHandlerLifetime(TimeSpan.FromMinutes(5));

Conclusion
High performance and scalability in ASP.NET Core are achieved through a combination of asynchronous design , caching , efficient data access , and smart infrastructure choices.
By applying the strategies discussed from optimizing middleware and Kestrel configuration to leveraging Redis and compression — your ASP.NET Core application can handle massive workloads with low latency and high reliability.

Building contemporary online apps and APIs is now easier, lighter, and faster thanks to ASP.NET Core's constant evolution. Developers benefit from significant advancements in OpenAPI integration and Minimal APIs with ASP.NET Core 10.0. With the help of technologies like Swagger UI, Postman, and client SDK generators, these enhancements improve developer experience, streamline API design, and decrease boilerplate. We'll examine what's new, why it matters, and how to make the most of these improvements in this post.

1. Understanding Minimal APIs
Minimal APIs were first introduced in .NET 6 to provide a lightweight way of creating HTTP APIs without the overhead of controllers, attributes, or complex routing. Instead, you define endpoints directly in your Program.cs file.

Here’s a basic minimal API example in .NET 10:
var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", () => "Hello, ASP.NET Core 10 Minimal APIs!");

app.Run();

Instead of controllers, the request handling logic is expressed inline. This reduces ceremony, making it ideal for:

• Microservices
• Prototypes and demos
• Lightweight REST APIs

2. What’s New in Minimal APIs in .NET 10
ASP.NET Core 10 builds on the foundation of Minimal APIs with:

• Route groups with conventions – Organize endpoints logically.
• Improved parameter binding – Cleaner support for complex types.
• OpenAPI (Swagger) auto-generation improvements – Richer metadata and validation.
• SSE (Server-Sent Events) – Real-time streaming support.
• Enhanced filters and middleware integration – Greater flexibility.

3. OpenAPI in ASP.NET Core 10
OpenAPI (formerly known as Swagger) is the industry standard for describing REST APIs. It enables:

• Documentation: Swagger UI lets developers explore APIs interactively.
• Client SDK generation: Auto-generate clients in C#, TypeScript, Python, etc.
• Validation: Ensures API contracts remain consistent.

In .NET 10, Microsoft has enhanced the OpenAPI package ( Microsoft.AspNetCore.OpenApi ) to work seamlessly with Minimal APIs .

4. Setting Up OpenAPI with Minimal APIs
Add the required package in your project file ( .csproj ):
<ItemGroup>
  <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="10.0.0" />
  <PackageReference Include="Swashbuckle.AspNetCore" Version="6.5.0" />
</ItemGroup>

Then configure it in Program.cs :
var builder = WebApplication.CreateBuilder(args);

// Add OpenAPI services
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

// Enable middleware for Swagger
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

// Define Minimal API endpoints
app.MapGet("/api/products", () =>
{
    return new[]
    {
        new Product(1, "Laptop", 1200),
        new Product(2, "Phone", 800)
    };
})
.WithName("GetProducts")
.WithOpenApi();

app.Run();

record Product(int Id, string Name, decimal Price);

Key Enhancements in .NET 10

• .WithOpenApi() automatically generates documentation for endpoints.
• Models ( Product ) are described in the OpenAPI schema.
• Swagger UI displays full details without extra configuration.

5. Route Groups in Minimal APIs
.NET 10 introduces Route Groups, which make organizing endpoints easier.
var products = app.MapGroup("/api/products");

products.MapGet("/", () =>
{
    return new List<Product>
    {
        new(1, "Tablet", 500),
        new(2, "Smartwatch", 200)
    };
})
.WithOpenApi();

products.MapGet("/{id:int}", (int id) =>
{
    return new Product(id, "Generated Product", 99.99m);
})
.WithOpenApi();

• All routes under /api/products are grouped.
• Swagger displays them neatly under a single section.

6. OpenAPI Metadata Enrichment
You can enrich OpenAPI docs using endpoint metadata:
products.MapPost("/", (Product product) =>
{
    return Results.Created($"/api/products/{product.Id}", product);
})
.WithName("CreateProduct")
.WithOpenApi(op =>
{
    op.Summary = "Creates a new product";
    op.Description = "Adds a product to the catalog with details like name and price.";
    return op;
});

This makes the Swagger UI highly descriptive with summaries and descriptions .

7. Complex Parameter Binding
Minimal APIs now support cleaner parameter binding.
products.MapPut("/{id:int}", (int id, ProductUpdate update) =>
{
    return Results.Ok(new Product(id, update.Name, update.Price));
})
.WithOpenApi();

record ProductUpdate(string Name, decimal Price);

• Complex request bodies like ProductUpdate are automatically parsed from JSON.
• OpenAPI correctly documents these models.

8. Filters in Minimal APIs
Filters add cross-cutting behaviors like validation or logging without middleware.
products.MapPost("/validate", (Product product) =>
{
    if (string.IsNullOrWhiteSpace(product.Name))
        return Results.BadRequest("Name is required");

    return Results.Ok(product);
})
.AddEndpointFilter(async (context, next) =>
{
    Console.WriteLine("Before executing endpoint");
    var result = await next(context);
    Console.WriteLine("After executing endpoint");
    return result;
})
.WithOpenApi();

Filters improve reusability, and OpenAPI reflects validation details.

9. Server-Sent Events (SSE) in Minimal APIs
Streaming real-time updates is now simpler:
app.MapGet("/notifications", async context =>
{
    context.Response.Headers.Add("Content-Type", "text/event-stream");
    for (int i = 1; i <= 5; i++)
    {
        await context.Response.WriteAsync($"data: Notification {i}\n\n");
        await context.Response.Body.FlushAsync();
        await Task.Delay(1000);
    }
}).WithOpenApi();

Swagger documents the endpoint, though SSE testing is best via Postman or browsers.

10. Security with OpenAPI
You can define security schemes like JWT Bearer authentication in Swagger.
builder.Services.AddSwaggerGen(options =>
{
    options.AddSecurityDefinition("Bearer", new OpenApiSecurityScheme
    {
        In = ParameterLocation.Header,
        Description = "Enter JWT with Bearer prefix",
        Name = "Authorization",
        Type = SecuritySchemeType.ApiKey
    });

    options.AddSecurityRequirement(new OpenApiSecurityRequirement
    {
        {
            new OpenApiSecurityScheme
            {
                Reference = new OpenApiReference
                {
                    Type = ReferenceType.SecurityScheme,
                    Id = "Bearer"
                }
            },
            Array.Empty<string>()
        }
    });
});

Swagger UI now includes a “Authorize” button for JWT authentication.

11. Benefits of OpenAPI & Minimal APIs in .NET 10

• Developer Productivity: Write fewer lines of code.
• Auto Documentation: Swagger/OpenAPI keeps docs updated.
• Integration Ready: Generate SDKs for Angular, React, Python, etc.
• Improved Testing: Swagger UI doubles as an interactive test client.
• Performance: Minimal APIs are faster to start and lighter than MVC controllers.

12. Example: Full Program.cs
var builder = WebApplication.CreateBuilder(args);

builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

var products = app.MapGroup("/api/products");

products.MapGet("/", () =>
    new List<Product>
    {
        new(1, "Laptop", 1200),
        new(2, "Phone", 800)
    })
.WithOpenApi();

products.MapPost("/", (Product product) =>
    Results.Created($"/api/products/{product.Id}", product))
.WithOpenApi(op =>
{
    op.Summary = "Create a new product";
    op.Description = "Adds a product with name and price to the catalog.";
    return op;
});

app.Run();

record Product(int Id, string Name, decimal Price);

Conclusion
ASP.NET Core 10.0 takes Minimal APIs and OpenAPI integration to the next level. Developers can now:

• Build lightweight APIs with minimal boilerplate.
• Automatically generate and enrich documentation.
• Organize endpoints better with route groups.
• Use filters for cross-cutting concerns.
• Stream updates via SSE.
• Secure APIs with built-in OpenAPI security definitions.

The combination of Minimal APIs and OpenAPI in .NET 10 ensures that APIs are not only fast and efficient but also well-documented, secure, and integration-friendly. This makes ASP.NET Core 10 a powerful choice for microservices, mobile backends, and modern web APIs.

In ASP.NET applications, the Web.config file is the heart of configuration. It allows us to define application settings, connection strings, error handling, session timeouts, security rules, and even URL rewriting without touching our C# backend code.

In this blog, we’ll explore:

• The concept of Web.config
• Redirect usage through Web.config
• Page protection and security settings
• URL rewriting for clean SEO-friendly URLs
• Frontend usages (single name, double name, third parameter, redirects)

And finally, we’ll go line by line through a real-world Web.config example.

What is Web.config?

• A special XML file used in ASP.NET applications.
• It defines configuration settings such as database connections, authentication, authorization, custom errors, and security headers.
• Stored at the root of the application.

What is <customErrors> in ASP.NET?

• <customErrors> is a configuration element in Web.config that controls how errors are handled and displayed in ASP.NET applications.
• Instead of showing raw ASP.NET/YELLOW ERROR PAGES (with stack trace), we can show friendly error pages (like Errorpage.aspx ).
• This improves user experience and also protects sensitive error details from hackers.

1. Three Ways (Modes) of Using <customErrors>
customErrors with Mode="Off" and Status Codes Defined

<customErrors mode="Off">
  <error statusCode="400" redirect="Errorpage.aspx" />
  <error statusCode="403" redirect="Errorpage.aspx" />
  <error statusCode="404" redirect="Errorpage.aspx" />
  <error statusCode="500" redirect="Errorpage.aspx" />
</customErrors>

Explanation

• mode="Off" → Application will display detailed ASP.NET error pages (stack trace, line numbers).
• But here, specific error code redirections are defined.
• If you visit a page that doesn’t exist → it redirects to Errorpage.aspx .
• This is generally useful in development environments, where you need to debug errors but also want some controlled redirections.
• If a 404 Not Found error occurs → User is redirected to Errorpage.aspx .
• If a 500 Internal Server Error occurs → Same redirection.

Purpose: Developer debugging + handling user-friendly redirects.

2. customErrors with Mode="Off" (Single Line)
<customErrors mode="Off"/>

Explanation

• Application will always show detailed error messages .
• No redirection is done.
• Useful only in local development/testing — never recommended for production.

Purpose: Debugging only (not secure).

3. customErrors with Mode="On"
<customErrors mode="On"/>

Explanation

• Application will hide detailed error messages.
• Instead, it will show friendly custom error pages (like Errorpage.aspx).
• Secure approach for production environments.

Purpose: Protect sensitive error details from users/hackers, show professional error pages.

Quick Comparison

Final Takeaway:

• Mode=Off → Developer Mode (debugging)
• Mode=On → Production Mode (secure, user-friendly)
• Mode=Off with status codes → Debugging + Controlled Redirection

Securing Pages with Web.config
Code Section
<validation validateIntegratedModeConfiguration="false"/>
<httpProtocol>
  <customHeaders>
    <remove name="X-AspNet-Version"/>
    <remove name="X-AspNetMvc-Version"/>
    <remove name="X-Powered-By"/>
    <add name="Body-Count" value="Ice-T"/>
    <add name="Access-Control-Allow-Credentials" value="true"/>
    <add name="Access-Control-Allow-Headers" value="content-type"/>
    <add name="X-Content-Type-Options" value="nosniff"/>
    <add name="X-XSS-Protection" value="1; mode=block"/>
    <add name="Cache-Control" value="no-cache, no-store, must-revalidate"/>
    <add name="X-Frame-Options" value="SAMEORIGIN"/>
    <add name="X-Permitted-Cross-Domain-Policies" value="none"/>
    <add name="Strict-Transport-Security" value="max-age=31536000; includeSubDomains"/>
    <add name="Permissions-Policy" value="accelerometer=(), camera=(), geolocation=(), gyroscope=(), magnetometer=(), microphone=(), payment=(), usb=()"/>
  </customHeaders>
</httpProtocol>

Line-by-Line Explanation
1. Validation Mode
<validation validateIntegratedModeConfiguration="false"/>

• Concept: Controls validation of the IIS Integrated Pipeline configuration.
• Why Required: Sometimes, older Web.config settings are not compatible with IIS 7+ Integrated Pipeline mode.
• Purpose: Setting false tells ASP.NET not to validate older settings → prevents unnecessary runtime errors.

2. Removing Headers (Information Disclosure Prevention)
<remove name="X-AspNet-Version"/>
<remove name="X-AspNetMvc-Version"/>
<remove name="X-Powered-By"/>

• Concept: By default, ASP.NET/IIS sends these headers in HTTP responses.
• Why required: Hackers can identify framework versions and target known vulnerabilities.
• Purpose: Security through obfuscation → don’t expose technology stack details.

3. Adding Custom Headers
a) Fake Header (Obfuscation / Branding)
<add name="Body-Count" value="Ice-T"/>

• Concept: Adds a custom header with an arbitrary value.
• Why Required: Not mandatory, but can be used for tracking or branding.
• Purpose: Demonstration/fun — here it’s "Ice-T" (artist’s name), doesn’t affect functionality.

b) CORS Headers (Cross-Origin Resource Sharing)
<add name="Access-Control-Allow-Credentials" value="true"/>
<add name="Access-Control-Allow-Headers" value="content-type"/>

Concept: Defines rules for cross-origin requests.
Why required: If your API is called from JavaScript on another domain.

Purpose

• Allow-Credentials=true → lets cookies/auth headers be sent in cross-domain requests.
• Allow-Headers=content-type → allows Content-Type header in requests.

c) Content Security Headers
<add name="X-Content-Type-Options" value="nosniff"/>

• Concept : Stops browsers from MIME-type sniffing.
• Why Required: Prevents malicious file uploads from being misinterpreted (e.g., .jpg running as script).
• Purpose: Protects against content-type-based attacks.

d) XSS Protection
<add name="X-XSS-Protection" value="1; mode=block"/>Concept: Activates the browser’s built-in XSS (Cross-Site Scripting) filter.

• Why Required: Prevents malicious scripts from executing in the browser.
• Purpose: Block pages if XSS is detected.

e) Cache Control
<add name="Cache-Control" value="no-cache, no-store, must-revalidate"/>

• Concept : Prevents caching of sensitive content.
• Why Required : Avoids storing confidential pages in browser/proxy cache.
• Purpose : Ensures always fresh content, good for banking/financial apps.

f) Clickjacking Protection
<add name="X-Frame-Options" value="SAMEORIGIN"/>

• Concept: Controls iframe embedding.
• Why Required: Attackers can load your site inside a hidden iframe and trick users (clickjacking).
• Purpose: Allows embedding only from the same domain.

g) Cross-Domain Policy
<add name="X-Permitted-Cross-Domain-Policies" value="none"/>

• Concept: Restricts Adobe Flash, PDF, or other plugins from making cross-domain requests.
• Why Required: Stops unauthorized access from plugins.
• Purpose: Set to none for strictest security.

h) Strict Transport Security (HSTS)
<add name="Strict-Transport-Security" value="max-age=31536000; includeSubDomains"/>

• Concept: Forces browser to use HTTPS for all requests.
• Why Required: Prevents downgrade attacks and cookie hijacking on HTTP.
• Purpose: Enforces HTTPS for 1 year ( 31536000 seconds ).

i) Permissions Policy (Feature Control)
<add name="Permissions-Policy" value="accelerometer=(), camera=(), geolocation=(), gyroscope=(), magnetometer=(), microphone=(), payment=(), usb=()"/>

• Concept: Controls access to powerful browser APIs.
• Why Required: Protects privacy by blocking unnecessary device features.
• Purpose: Disables camera, microphone, location, USB, etc., unless explicitly allowed.

No application is completely impervious to security risks. Even with the finest safe coding techniques, vulnerabilities, configuration errors, and third-party dependencies can still be exploited by attackers. To promptly identify, address, and recover from security breaches, each ASP.NET Core application needs a clear Incident Response Plan (IRP).

The procedures, resources, and sample code for creating an incident response plan designed especially for ASP.NET Core applications are all covered in this article.

What Is an Incident Response Plan?
An Incident Response Plan (IRP) is a documented, structured approach to handling security breaches. Its purpose is to:

• Detect suspicious or malicious activity quickly.
• Contain and mitigate damage.
• Eradicate the root cause of the breach.
• Recover normal operations.
• Learn from incidents to prevent future breaches.
• Key Phases of Incident Response in ASP.NET Core

1. Preparation
Before a breach happens, ensure:

• Security logging and monitoring are enabled.
• Alerts are configured for unusual activities (e.g., failed logins, suspicious API calls).
• Teams know their roles and escalation paths.
• Backups and recovery procedures are in place.

Example: Enable structured security logging with Serilog or Application Insights:
Log.Logger = new LoggerConfiguration()
    .Enrich.FromLogContext()
    .WriteTo.Console()
    .WriteTo.File("logs/security-.log", rollingInterval: RollingInterval.Day)
    .CreateLogger();

2. Identification
Detect and confirm the breach.
Common signs in ASP.NET Core apps include:

• Multiple failed login attempts (brute force).
• Unauthorized access to protected endpoints.
• Sudden spikes in API traffic (possible DoS).
• Unexpected changes in configuration or database.

Example: Log and flag repeated failed logins:
_logger.LogWarning("Failed login attempt {Count} for {Username} from {IP}",
                   attemptCount, username, ip);
if (attemptCount > 5)
{
    _logger.LogError("Possible brute-force attack detected from IP {IP}", ip);
    // Trigger an alert or block IP temporarily
}

3. Containment
Limit the scope of the breach while keeping services running.
Disable compromised accounts.

Block malicious IPs temporarily.

Isolate affected microservices or APIs.

Example: Blocking an IP using ASP.NET Core middleware:
public class IpBlockMiddleware
{
    private readonly RequestDelegate _next;
    private static readonly HashSet<string> BlockedIps = new();

    public IpBlockMiddleware(RequestDelegate next) => _next = next;

    public async Task Invoke(HttpContext context)
    {
        var ip = context.Connection.RemoteIpAddress?.ToString();
        if (BlockedIps.Contains(ip))
        {
            context.Response.StatusCode = 403;
            await context.Response.WriteAsync("Access denied.");
            return;
        }

        await _next(context);
    }

    public static void BlockIp(string ip) => BlockedIps.Add(ip);
}

4. Eradication
Remove the root cause of the breach.

• Patch vulnerable dependencies (e.g., NuGet packages).
• Fix misconfigured CORS, authentication, or authorization policies.
• Remove injected malicious code or unauthorized files.

Use OWASP Dependency Check or dotnet list package --outdated to identify vulnerabilities.

5. Recovery
Restore services to normal operations.

• Rotate compromised keys, tokens, or certificates.
• Restore data from clean backups if tampered with.
• Gradually reintroduce blocked IPs/users after ensuring safety.
• Monitor closely for recurrence.

6. Lessons Learned
After the incident, perform a post-mortem analysis:

• What was the root cause?
• How was it detected?
• Were response times acceptable?
• What controls can prevent recurrence?

Document findings and improve the incident response playbook.

Automating Incident Response in ASP.NET Core
You can integrate automated workflows for faster response:

• Azure Sentinel or AWS GuardDuty—Automatically trigger alerts and block malicious IPs.
• Webhook-based alerts – Notify your team on Slack/Teams when security anomalies occur.
• Custom ASP.NET Core filters—Enforce consistent logging and security checks across controllers.

Example: Global exception logging with IExceptionFilter:
public class SecurityExceptionFilter : IExceptionFilter
{
    private readonly ILogger<SecurityExceptionFilter> _logger;

    public SecurityExceptionFilter(ILogger<SecurityExceptionFilter> logger)
    {
        _logger = logger;
    }

    public void OnException(ExceptionContext context)
    {
        _logger.LogError(context.Exception,
                         "Security exception at {Path}",
                         context.HttpContext.Request.Path);
    }
}

Incident Response Checklist for ASP.NET Core Apps

• Enable detailed, structured security logging.
• Monitor logs using SIEM tools (Azure Sentinel, ELK, Splunk).
• Configure alerts for brute-force and suspicious activity.
• Implement containment mechanisms (IP blocking, account disabling).
• Regularly patch dependencies and frameworks.
• Practice recovery via backups and incident simulations.
• Conduct post-incident reviews and update your IRP.

Conclusion
A well-prepared incident response plan ensures that your ASP.NET Core applications can withstand breaches and recover with minimal damage. By combining proactive monitoring, structured logging, automated containment, and post-incident learning, your development and security teams can respond to threats effectively.

The Data Protection API (DPAPI), which is included into ASP.NET Core, offers developers easy, safe, and expandable cryptographic operations. The framework itself makes extensive use of it internally, for instance, to safeguard OAuth state, CSRF tokens, and authentication cookies. This post describes how to use ASP.NET Core's Data Protection APIs to safeguard your private information.

The Data Protection API: What is it?
ASP.NET Core's Data Protection API is a cryptography framework made to:

• Encrypt and decrypt data, such as tokens and connection strings.
• Securely handle keys (with support for key rotation).
• Assure confidentiality and resistance to tampering.
• Connect with ASP.NET Core components with ease.

You depend on a managed service that takes care of algorithm selection, key management, and lifetime automatically rather than handling cryptography by yourself.

Setting Up Data Protection in ASP.NET Core
The Data Protection service is registered within Program.cs or Startup.cs.
var builder = WebApplication.CreateBuilder(args);

// Register Data Protection services
builder.Services.AddDataProtection();

builder.Services.AddControllers();
var app = builder.Build();
app.MapControllers();
app.Run();

This sets up the Data Protection system with in-memory key storage (by default).

Protecting and Unprotecting Data
Create a service that uses the IDataProtector interface:
using Microsoft.AspNetCore.DataProtection;

public class EncryptionService
{
    private readonly IDataProtector _protector;

    public EncryptionService(IDataProtectionProvider provider)
    {
        // Create a protector with a unique purpose string
        _protector = provider.CreateProtector("MyApp.DataProtection.Demo");
    }

    public string Protect(string plainText)
    {
        return _protector.Protect(plainText);
    }

    public string Unprotect(string protectedData)
    {
        return _protector.Unprotect(protectedData);
    }
}

Register it in Program.cs:
builder.Services.AddScoped<EncryptionService>();

Usage in a controller:
[ApiController]
[Route("api/[controller]")]
public class SecureController : ControllerBase
{
    private readonly EncryptionService _encryptionService;

    public SecureController(EncryptionService encryptionService)
    {
        _encryptionService = encryptionService;
    }

    [HttpGet("protect")]
    public string ProtectData(string input)
    {
        return _encryptionService.Protect(input);
    }

    [HttpGet("unprotect")]
    public string UnprotectData(string input)
    {
        return _encryptionService.Unprotect(input);
    }
}

Persisting Keys (Production Scenarios)
By default, keys are stored in-memory and lost when the app restarts. For production, configure persistent key storage.

File System Storage
builder.Services.AddDataProtection()
    .PersistKeysToFileSystem(new DirectoryInfo(@"C:\keys"))
    .SetApplicationName("MyApp");

Azure Blob Storage
builder.Services.AddDataProtection()
    .PersistKeysToAzureBlobStorage(
        new Uri("https://<account>.blob.core.windows.net/keys/key.xml"),
        new DefaultAzureCredential());

Redis (for multiple instances)
builder.Services.AddDataProtection()
    .PersistKeysToStackExchangeRedis(connectionMultiplexer, "DataProtection-Keys");

Key Management and Rotation

• Keys are automatically rotated every 90 days (configurable).
• Old keys are retained for decrypting data.
• You can manually configure key lifetimes:

builder.Services.AddDataProtection()
    .SetDefaultKeyLifetime(TimeSpan.FromDays(30));

Common Use Cases

• Protecting sensitive settings (e.g., API keys).
• Encrypting tokens or IDs before sending them in URLs.
• Securing cookies and session state (handled automatically).
• Multi-instance apps (persist keys to shared storage).

Best Practices

• Always persist keys in production.
• Use a unique purpose string for each protected data type.
• Store keys in secure locations (Azure Key Vault, Blob Storage, Redis).
• Rotate keys regularly.
• Never hardcode secrets—use environment variables or secret managers.

Conclusion
The ASP.NET Core Data Protection API provides a secure and developer-friendly way to handle encryption without needing deep cryptography knowledge. Whether you’re protecting sensitive values in configuration, encrypting tokens, or securing cookies, the Data Protection system ensures your app stays resilient against common cryptographic pitfalls. With persistent key storage, key rotation, and integration with cloud services, it’s ready for enterprise-grade applications.

Thousands of requests per second are frequently made to APIs. Excessive traffic, whether malicious (DoS/DDoS) or accidental (clients flooding with requests), can cause system failure, raise expenses, or impair performance if sufficient controls are not in place. Techniques like rate limitation and throttling are essential for managing API usage, guaranteeing equitable resource allocation, and safeguarding backend services.

This post will explain how to use built-in middleware (from.NET 7+), bespoke solutions, and recommended practices to establish rate restriction in ASP.NET Core Web APIs.

What is rate limiting?
Rate limiting defines how many requests a client (IP, user, or token) can make in a given time window.

For example

• Limit: 100 requests per minute per client.
• If exceeded, the API returns HTTP 429 Too Many Requests.

What is throttling?
Throttling goes beyond rate limiting. Instead of outright rejecting requests, it can:

• Queue or delay requests until capacity is available.
• Reduce service quality for heavy users while maintaining fairness.
• Apply dynamic limits based on client type (free vs. premium).

Benefits of Rate Limiting & Throttling

• Prevent abuse (scraping, brute-force attacks).
• Protect backend systems from overload.
• Ensure fair use among consumers.
• Support tiered plans (e.g., free users: 50 requests/min, premium: 500 requests/min).

Implementing Rate Limiting in ASP.NET Core
1. Using .NET 7+ Built-in Rate Limiting Middleware
ASP.NET Core 7 introduced a dedicated rate-limiting middleware.

Install Package
If you’re on .NET 7+:
dotnet add package Microsoft.AspNetCore.RateLimiting

Configure in Program.cs
using System.Threading.RateLimiting;
using Microsoft.AspNetCore.RateLimiting;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddRateLimiter(options =>
{
    // Limit each client to 100 requests per minute
    options.AddFixedWindowLimiter("Fixed", opt =>
    {
        opt.PermitLimit = 100;
        opt.Window = TimeSpan.FromMinutes(1);
        opt.QueueProcessingOrder = QueueProcessingOrder.OldestFirst;
        opt.QueueLimit = 2; // Max queued requests
    });
});

var app = builder.Build();

app.UseRateLimiter();

app.MapGet("/api/data", () => "This is a rate-limited endpoint")
   .RequireRateLimiting("Fixed");

app.Run();

2. Token Bucket Limiter Example
This allows burst traffic while enforcing overall limits.
options.AddTokenBucketLimiter("TokenBucket", opt =>
{
    opt.TokenLimit = 50;                 // Max tokens
    opt.QueueLimit = 2;
    opt.ReplenishmentPeriod = TimeSpan.FromSeconds(10);
    opt.TokensPerPeriod = 10;            // Refill rate
    opt.AutoReplenishment = true;
});

3. Sliding Window Limiter Example
Smooths out spikes by distributing requests across sliding intervals.
options.AddSlidingWindowLimiter("SlidingWindow", opt =>
{
    opt.PermitLimit = 100;
    opt.Window = TimeSpan.FromMinutes(1);
    opt.SegmentsPerWindow = 6; // 10 sec segments
    opt.QueueLimit = 2;
});

4. Per-User or Per-API Key Limiting
You can bind rate limits to users, API keys, or IPs.
builder.Services.AddRateLimiter(options =>
{
    options.GlobalLimiter = PartitionedRateLimiter.Create<HttpContext, string>(httpContext =>
    {
        var userId = httpContext.User?.Identity?.Name ?? "anonymous";
        return RateLimitPartition.GetFixedWindowLimiter(userId, _ => new FixedWindowRateLimiterOptions
        {
            PermitLimit = 10,
            Window = TimeSpan.FromSeconds(30)
        });
    });
});

Handling 
Exceeded Limits
When a client exceeds the allowed requests, ASP.NET Core automatically returns:
HTTP/1.1 429 Too Many Requests
Retry-After: 60

You can customize the response:
options.OnRejected = (context, token) =>
{
    context.HttpContext.Response.StatusCode = StatusCodes.Status429TooManyRequests;
    return context.HttpContext.Response.WriteAsync("Too many requests. Please try again later.");
};

Implementing Throttling (Delaying Requests)
Instead of rejecting requests, you can queue and delay them.
options.AddFixedWindowLimiter("Throttle", opt =>
{
    opt.PermitLimit = 5;
    opt.Window = TimeSpan.FromSeconds(10);
    opt.QueueLimit = 5;
    opt.QueueProcessingOrder = QueueProcessingOrder.OldestFirst;
});

Here, extra requests wait in a queue instead of failing immediately.

Best Practices for Rate Limiting

• Apply limits per identity, not globally (use API key, user, or IP).
• Different plans for different clients (free vs. premium tiers).
• Monitor & log 429 responses to detect abuse.
• Return Retry-After headers so clients can back off.
• Combine with API Gateway (e.g., YARP, NGINX, Azure API Management) for distributed systems.
• Always test under load scenarios to fine-tune values.

Example: Full ASP.NET Core Web API with Rate Limiting
using System.Threading.RateLimiting;
using Microsoft.AspNetCore.RateLimiting;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers();
builder.Services.AddRateLimiter(options =>
{
    options.AddFixedWindowLimiter("ApiLimiter", opt =>
    {
        opt.PermitLimit = 100;
        opt.Window = TimeSpan.FromMinutes(1);
        opt.QueueLimit = 0;
    });

    options.OnRejected = async (context, _) =>
    {
        context.HttpContext.Response.StatusCode = 429;
        await context.HttpContext.Response.WriteAsync("Too many requests. Slow down!");
    };
});

var app = builder.Build();

app.UseHttpsRedirection();
app.UseAuthorization();

app.UseRateLimiter();

app.MapControllers().RequireRateLimiting("ApiLimiter");

app.Run();

Conclusion
Rate limiting and throttling are essential to keep your ASP.NET Core Web API secure, stable, and fair. With .NET 7’s built-in middleware, you can easily configure fixed, sliding, or token bucket rate limits. For advanced needs, combine them with per-user throttling, API gateways, and monitoring to maintain performance and reliability.

Cookies are frequently used by web applications to preserve user sessions following authentication. However, attackers can assume user identities and obtain illegal access if cookies are stolen or compromised. Two of the most prevalent attack methods in contemporary online applications are session hijacking and cookie theft. The recommended methods for preventing session hijacking in ASP.NET Core will be discussed in this post.

What is session hijacking?

• Session hijacking is when an attacker takes over a valid session by stealing session cookies. This can be done via:
• XSS (Cross-Site Scripting) → Injecting malicious JavaScript to steal cookies
• Packet Sniffing → Intercepting cookies over insecure HTTP connections
• Session Fixation → Forcing a user to use a known session ID
• Man-in-the-Middle Attacks → Capturing cookies during transmission

Once an attacker gets hold of a session cookie, they can act as a legitimate user.

ASP.NET Core Built-in Protections
ASP.NET Core provides mechanisms to secure cookies and reduce hijacking risks. Let’s see how to configure them.

1. Use Secure Cookies
Ensure cookies are only sent over HTTPS and not accessible via JavaScript.
builder.Services.ConfigureApplicationCookie(options =>
{
    options.Cookie.HttpOnly = true; // Prevent JavaScript access
    options.Cookie.SecurePolicy = CookieSecurePolicy.Always; // HTTPS only
    options.Cookie.SameSite = SameSiteMode.Strict; // Prevent CSRF
});

Best Practice: Always enforce HTTPS using app.UseHttpsRedirection();.

2. Short Session Lifetimes with Sliding Expiration
Short-lived cookies minimize the attack window.
builder.Services.ConfigureApplicationCookie(options =>
{
    options.ExpireTimeSpan = TimeSpan.FromMinutes(20);
    options.SlidingExpiration = true; // Refresh on activity
});

3. Regenerate Session IDs on Login
Prevent session fixation by regenerating identifiers after login.
await _signInManager.SignInAsync(user, isPersistent: false);
await _context.SaveChangesAsync();

ASP.NET Core Identity automatically issues a new cookie upon sign-in, mitigating fixation attacks.

4. Implement Cookie Authentication Validation
Periodically validate security stamps to invalidate stolen cookies.
builder.Services.Configure<SecurityStampValidatorOptions>(options =>
{
    options.ValidationInterval = TimeSpan.FromMinutes(5);
});

This ensures that if a user changes their password or logs out, old cookies become invalid.

5. Use SameSite Cookies Against CSRF
SameSite prevents cookies from being sent in cross-site requests.
options.Cookie.SameSite = SameSiteMode.Strict;

If your app requires cross-site cookies (e.g., external login providers), consider SameSite=Lax but avoid None unless absolutely necessary (and always use HTTPS).

6. Protect Against XSS (Cross-Site Scripting)
Since XSS is a common way to steal cookies:

•     Encode all output (@Html.Encode() or Razor automatic encoding).
•     Use Content Security Policy (CSP).
•     Sanitize user inputs.

In Program.cs:
app.Use(async (context, next) =>
{
    context.Response.Headers.Add("Content-Security-Policy", "default-src 'self'");
    await next();
});

7. Enforce Re-authentication for Sensitive Actions
For critical operations (password change, payment, deleting account), force users to re-enter credentials or MFA.
var user = await _signInManager.GetTwoFactorAuthenticationUserAsync();
if (user == null)
{
    return RedirectToAction("Login");
}

8. Use Multi-Factor Authentication (MFA)
Even if cookies are stolen, requiring a second factor makes hijacking much harder.

9. Monitor and Revoke Compromised Sessions
Log user login locations, devices, and IPs. Allow users (and admins) to view and revoke active sessions.
await _signInManager.SignOutAsync(); // Invalidate cookie

Conclusion
Session hijacking and cookie theft are real threats, but ASP.NET Core provides strong tools to mitigate them.
To secure your app:

• Always use HTTPS with secure, HttpOnly, and SameSite cookies.
• Shorten cookie lifetimes and use sliding expiration.
• Regenerate session IDs after login and validate security stamps.
• Defend against XSS and CSRF attacks.
• Enforce MFA and re-authentication for sensitive operations.

By combining these techniques, you can significantly reduce the attack surface and protect your users.

JSON injection: what is it?

• When an attacker modifies a JSON payload's structure to add unexpected keys, values, or scripts, this is known as JSON injection.
• Attackers take advantage of
  • Additional fields (such as isAdmin: true).
  • JSON string script injection (which, if done incorrectly, can result in XSS).
  • JSON was altered to avoid validations or to cause parser crashes.

An example of an attack payload

Example Attack Payload
{
"username": "attacker",
"email": "[email protected]",
"isAdmin": true,        // Sensitive field injection
"__proto__": { "polluted": "yes" } // Prototype pollution attack
}

If your API model-binds this blindly into your entity, attackers can escalate privileges or poison objects.

Risks of Malformed JSON

• Denial of Service (DoS): Sending enormous JSON payloads.
• Deserialization flaws: Exploiting weak parsers (e.g., type confusion).
• Validation bypass: Sending unexpected JSON structures.

How to Protect in ASP.NET Core?

1. Use DTOs Instead of Entities
Never accept raw JSON into entity models. Define Data Transfer Objects (DTOs) with strict fields.
public class RegisterDto
{
[Required, StringLength(50)]
public string Username { get; set; }

[Required, EmailAddress]
public string Email { get; set; }

[Required, StringLength(100)]
public string Password { get; set; }
}

Controller
[HttpPost("register")]
public IActionResult Register([FromBody] RegisterDto dto)
{
if (!ModelState.IsValid)
    return BadRequest(ModelState);

// Safe mapping
var user = new User
{
    Username = dto.Username,
    Email = dto.Email,
    IsAdmin = false // Explicitly controlled
};

return Ok(user);
}

Prevents attackers from injecting extra JSON properties, such as isAdmin.

2. Reject Unknown Properties
By default, System. Text.Json ignores unknown fields. Force it to fail on unknown JSON properties.
builder.Services.AddControllers()
.AddJsonOptions(options =>
{
options.JsonSerializerOptions.ReadCommentHandling = JsonCommentHandling.Disallow;
options.JsonSerializerOptions.AllowTrailingCommas = false;
options.JsonSerializerOptions.UnknownTypeHandling = System.Text.Json.Serialization.JsonUnknownTypeHandling.Fail;
options.JsonSerializerOptions.PropertyNameCaseInsensitive = false;
});

Or, in Newtonsoft.Json.
builder.Services.AddControllers()
.AddNewtonsoftJson(options =>
{
options.SerializerSettings.MissingMemberHandling = Newtonsoft.Json.MissingMemberHandling.Error;
});

Any unexpected JSON field will cause a 400 Bad Request.

3. Input Validation
Use Data Annotations or FluentValidation to validate JSON payloads.
if (!ModelState.IsValid)
return BadRequest(ModelState);

Ensures malformed JSON (wrong type, missing field) gets rejected.

4. Limit Request Size (Prevent DoS)
Attackers may send gigantic JSON payloads to crash your server. Set max request body size.
app.Use(async (context, next) =>
{
context.Request.Headers.ContentLength = Math.Min(context.Request.ContentLength ?? 0, 10_000); // 10 KB
await next();
});

Or in Kestrel
builder.WebHost.ConfigureKestrel(options =>
{
options.Limits.MaxRequestBodySize = 10 * 1024; // 10 KB
});

Protects against payload flooding.

5. Sanitize JSON String Fields
Attackers may inject <script> or SQL-like payloads inside JSON strings. Use HtmlSanitizer or encoding before saving.
var sanitizer = new HtmlSanitizer();
dto.Username = sanitizer.Sanitize(dto.Username);

Prevents XSS when storing/displaying JSON fields.
6. Strong Content-Type Validation
Reject requests that are not application/json.

if (!context.Request.ContentType?.Contains("application/json") ?? true)
{
context.Response.StatusCode = StatusCodes.Status415UnsupportedMediaType;
return;
}

Stops attackers from sneaking payloads with wrong MIME types.
7. Use JsonDocument for Strict Parsing
If you don’t trust the payload at all, parse manually.
using var doc = JsonDocument.Parse(jsonString, new JsonDocumentOptions
{
AllowTrailingCommas = false,
CommentHandling = JsonCommentHandling.Disallow
});

if (!doc.RootElement.TryGetProperty("username", out var username))
return BadRequest("Missing username");

Complete control over parsing logic.

8. Audit & Logging
Log rejected payloads with correlation IDs.
_logger.LogWarning("Invalid JSON payload received: {Payload}", jsonString);

Helps detect attack attempts.

Best Practices Checklist

• Use DTOs (never bind entities).
• Fail on unknown JSON properties.
• Validate input with Data Annotations/FluentValidation.
• Set max request body size to prevent DoS.
• Sanitize string fields for XSS safety.
• Enforce application/json Content-Type.
• Parse manually ( JsonDocument ) for untrusted payloads.
• Log and monitor invalid payload attempts.

Conclusion
ASP.NET Core provides strong defenses, but developers must explicitly enable strict JSON parsing and validation.
By using DTOs, rejecting unknown fields, sanitizing input, and setting request limits, you protect your API from.

• JSON Injection
• Malformed Payload DoS
• Prototype Pollution
• XSS inside JSON

To guarantee accuracy and lower failure rates in digital payment systems, a UPI (Unified Payments Interface) ID must be validated before a transaction is started. Without revealing any critical implementation details, this article describes how to integrate a UPI ID validation API using JavaScript and C# (ASP.NET). To demonstrate, we'll use a fictitious endpoint.

Why Validate UPI IDs?

• Avoid transaction failures due to incorrect UPI IDs
• Improve user experience by providing real-time feedback
• Ensure the UPI ID belongs to the correct customer

Technologies Used

• C# (ASP.NET WebForms/Backend)
• JavaScript (AJAX for frontend calls)
• JSON for data communication
• Dummy API endpoint (replace with actual provider)

Example API Request
POST https://dummyapi.example.com/v1/payments/validate/vpa
Content-Type: application/json
{
"vpa": "user123@dummyupi"
}

Successful Response
{
  "vpa": "user123@dummyupi",
  "customer_name": "John Doe",
  "success": true
}

Invalid UPI Response
{
  "error": {
    "code": "BAD_REQUEST_ERROR",
    "description": "Invalid VPA. Please enter a valid Virtual Payment Address",
    "source": "customer",
    "step": "payment_initiation",
    "reason": "invalid_vpa"
  }
}

Backend Implementation (C#)
Here’s a simplified C# function to validate a UPI ID via HTTP POST.
public static string ValidateUPIID(string upi)
{
string responseJson = "";
try
{
    var requestObj = new { vpa = upi };
    string requestJson = new JavaScriptSerializer().Serialize(requestObj);

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://dummyapi.example.com/v1/payments/validate/vpa");
    request.Method = "POST";
    request.ContentType = "application/json";

    byte[] data = Encoding.UTF8.GetBytes(requestJson);
    using (var stream = request.GetRequestStream())
    {
        stream.Write(data, 0, data.Length);
    }

    using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
    using (StreamReader reader = new StreamReader(response.GetResponseStream()))
    {
        responseJson = reader.ReadToEnd();
    }

    if (responseJson.Contains("success"))
    {
        var jsonObj = new JavaScriptSerializer().Deserialize<UPIResponse>(responseJson);
        return jsonObj.success ? $"success - {jsonObj.customer_name}" : "failed - ";
    }
    else if (responseJson.Contains("error"))
    {
        var errorObj = new JavaScriptSerializer().Deserialize<UPIErrorResponse>(responseJson);
        string errDesc = !string.IsNullOrEmpty(errorObj.error.description) ? errorObj.error.description : "Invalid VPA";
        string errReason = !string.IsNullOrEmpty(errorObj.error.reason) ? errorObj.error.reason : "invalid_vpa";
        return $"reason - {errDesc} - {errReason}";
    }

    return "failed - unknown error";
}
catch (Exception ex)
{
    return "error - " + ex.Message;
}
}

public class UPIResponse
{
public string vpa { get; set; }
public string customer_name { get; set; }
public bool success { get; set; }
}
public class UPIErrorResponse
{
public UPIError error { get; set; }
}
public class UPIError
{
public string code { get; set; }
public string description { get; set; }
public string source { get; set; }
public string step { get; set; }
public string reason { get; set; }
}

JavaScript Frontend (AJAX Call)
<div class="bid-content-common bid-content-3">
<label class="upiid-lble">UPI ID</label>
<input id="txtupiid" runat="server" type="text" placeholder="Enter the UPI ID"
       onchange="UPIIDtxtboxchanges()" onblur="handleBlur()" />
<span id="upidtxt"></span>
<input id="upidvalidation" type="hidden" />
<button id="applybtn">Apply</button>
</div>

<script>
function UPIIDtxtboxchanges() {
    var applybtn = document.getElementById("applybtn");
    var upitxt = document.getElementById("upidvalidation");
    var txtbutton = document.getElementById("txtupiid");
    var verifytxt = document.getElementById("upidtxt");

    upitxt.value = 'Verify';
    upitxt.style.backgroundColor = "#F0F0F0";
    upitxt.style.border = "2px solid #979F6E";
    upitxt.style.color = "black";
    verifytxt.innerText = "";
    applybtn.style.pointerEvents = "auto";
}

function handleBlur() {
    // Assuming upivalidationmethod takes a callback function
    upivalidationmethod(function (isValid) {
        if (isValid) {
            return true;
        } else {
            return false;
        }
    });
}

function upivalidationmethod(callback) {
    var upiId = document.getElementById("upiInput").value;

    $.ajax({
        type: "POST",
        url: "/your-page.aspx/ValidateUPI",
        contentType: "application/json; charset=utf-8",
        data: JSON.stringify({ upi: upiId }),
        success: function (res) {
            var status = res.d.split('-');
            if (status[0] === "success") {
                $("#message").text("Valid UPI: " + status[1]).css("color", "green");
                callback(true);
            } else {
                $("#message").text("Invalid UPI").css("color", "red");
                callback(false);
            }
        },
        error: function () {
            $("#message").text("Error validating UPI").css("color", "red");
            callback(false);
        }
    });
}
</script>

Best Practices

• Always encrypt sensitive credentials used in API headers.
• Validate and sanitize inputs to avoid injection or malformed requests.
• Log and monitor UPI validation failures for system analysis.

Conclusion
Including a UPI ID validation phase in your application guarantees a better user experience, fewer unsuccessful transactions, and more seamless payments. This procedure is made more efficient by using an API, which provides error handling and real-time customer name checks. Securely in production, substitute your real provider's information with the fake API URL and login credentials.