Best Practices for Building Secure APIs in .NET Core

Building secure APIs in .NET Core requires a multi-layered approach involving authentication, authorization, data validation, encryption, and secure deployment practices. Here are the best practices for building secure APIs in .NET Core:

🔐 1. Use HTTPS

Always enforce HTTPS to encrypt data in transit.

Enforce HTTPS redirection in Startup.cs:

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app.UseHttpsRedirection();

Use HSTS (HTTP Strict Transport Security) in production.

🔐 2. Authentication & Authorization

✅ Use ASP.NET Core Identity or OAuth

Use JWT (JSON Web Tokens) for stateless authentication.

For complex scenarios, integrate with OAuth2 / OpenID Connect using IdentityServer or Azure AD.

✅ Protect Endpoints with [Authorize]

Restrict access at the controller or action level:

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[Authorize]

public class SecureController : ControllerBase

✅ Use Role-Based or Policy-Based Authorization

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services.AddAuthorization(options =>

{

    options.AddPolicy("AdminOnly", policy => policy.RequireRole("Admin"));

});

🛡️ 3. Input Validation and Model Binding

Use Data Annotations to validate models.

Sanitize inputs to prevent injection attacks (e.g., SQL Injection, XSS).

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[Required]

[StringLength(100)]

public string Name { get; set; }

Return appropriate status codes for invalid input (e.g., 400 Bad Request).

🔒 4. Secure Sensitive Data

✅ Use Secret Manager for local development:

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dotnet user-secrets init

dotnet user-secrets set "Jwt:Key" "your_secret"

✅ Store production secrets in secure storage:

Azure Key Vault

AWS Secrets Manager

Environment variables

🔍 5. Implement Logging & Monitoring

Use built-in logging (ILogger<T>) to capture events.

Mask sensitive data (e.g., passwords, API keys) in logs.

Integrate with monitoring tools (e.g., Application Insights, Serilog, ELK).

🚫 6. Prevent Common Attacks

✅ CSRF (Cross-Site Request Forgery)

Not typically an issue with APIs, but use [ValidateAntiForgeryToken] for forms.

✅ XSS (Cross-Site Scripting)

Avoid returning raw HTML; use JSON and proper escaping.

Sanitize inputs and outputs.

✅ SQL Injection

Always use Entity Framework Core or parameterized queries.

🧱 7. Rate Limiting and Throttling

Prevent abuse with rate limiting.

Use middleware like:

AspNetCoreRateLimit

🧪 8. Use Security Headers

Set HTTP security headers using middleware like NWebsec:

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app.UseHsts();

app.UseXContentTypeOptions();

app.UseReferrerPolicy(opts => opts.NoReferrer());

app.UseXXssProtection(opts => opts.EnabledWithBlockMode());

🔁 9. Version Your API

Use route versioning or header-based versioning:

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[Route("api/v1/[controller]")]

📦 10. Update Dependencies

Keep .NET Core, NuGet packages, and middleware up to date.

Use tools like dotnet list package --outdated.

✅ Final Checklist

 HTTPS enforced

 JWT / OAuth2 authentication

 Role/Policy-based authorization

 Input validation

 No hard-coded secrets

 Logging and monitoring

 Protection against common attacks

 Rate limiting in place

 API versioning implemented

 Up-to-date packages and dependencies

Learn Full Stack Dot NET Training in Hyderabad

Read More

Managing Dependencies with Dependency Injection in .NET

Error Handling and Logging in ASP.NET Core Applications

Implementing Authentication and Authorization in .NET Core Apps

How to Use Entity Framework Core for Database Management in Full Stack .NET

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