APIs (Application Programming Interfaces) are like the connectors or bridges that help software systems talk to each other. They allow apps to share data, connect services, and perform tasks across devices. From mobile apps to big cloud platforms, APIs power it all.

 

But here’s the problem — if APIs are not secure, hackers can easily break into your system. They can steal private user data, damage your app, or even take over parts of your business systems.

 

This guide will walk you through simple steps to keep your APIs safe from common problems that many developers face today.

 

 

 

 

It means verifying who is making the request. For example, when a user logs in with a username and password — that's authentication.

 

 

• Use OAuth 2.0 or OpenID Connect (OIDC) for secure logins.

• Use JWT (JSON Web Tokens) for stateless and safe user verification.

• Don't depend only on API keys — they can be stolen or shared. Combine them with proper login systems.

services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddJwtBearer(options =>
    {
        options.Authority = "https://your-auth-server.com";
        options.Audience = "your-api";
    });

 

This code lets your .NET app trust a specific login server and accept requests only from users who are allowed.

What is Authorization?

Use Role-Based Access Control (RBAC)

Only let users do what their role allows.

[Authorize(Roles = "Admin")]
public IActionResult GetSensitiveData()
{
    return Ok("Sensitive Data");
}

 

2. Always Use HTTPS to Encrypt Data

app.UseHttpsRedirection();

Also, keep your SSL/TLS certificates updated and redirect all HTTP (non-secure) traffic to HTTPS.

3. Protect Your API from SQL Injection

Safe Example Using Entity Framework:

var user = context.Users.FirstOrDefault(u => u.Email == email);

 

Unsafe Example:

var query = $"SELECT * FROM Users WHERE Email = '{email}'";

In the bad example above, if someone types a dangerous email string like email@example.com' OR '1'='1, they could trick your app into giving them access to everything.

4. Set Rate Limits to Block Spam and Overload Attacks

Example in ASP.NET Core:

services.AddRateLimiter(options =>
{
    options.AddFixedWindowLimiter("default", o =>
    {
        o.Window = TimeSpan.FromMinutes(1);
        o.PermitLimit = 100;
    });
});

This code means: only allowing 100 requests per minute from a single user.

5. Always Validate and Sanitize Input

Use Data Annotations for Validation

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

This makes sure the user has to enter a proper email address.

 

Sanitize User Input

Remove or escape dangerous characters before using input data:

var sanitizedInput = WebUtility.HtmlEncode(userInput);

This helps avoid attacks like XSS (Cross-Site Scripting).

6. Secure Your API with CORS Policies

Example:

services.AddCors(options =>
{
    options.AddPolicy("AllowSpecificOrigin", builder =>
        builder.WithOrigins("https://trusted-domain.com")
               .AllowAnyMethod()
               .AllowAnyHeader());
});

This stops others from misusing your API in a browser.

7. Log and Monitor All API Activity

Start with Basic Logging:

var logger = LoggerFactory.Create(builder => builder.AddConsole()).CreateLogger("API Logger");
logger.LogInformation("User login attempt detected");

 

Use Monitoring Tools:

Example:

[ApiVersion("1.0")]
[Route("api/v{version:apiVersion}/users")]
public class UsersController : ControllerBase { }

This lets you support v1, v2, etc. safely.

Conclusion

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