Handle CORS Error ASP.Net MVC

What is CORS?

CORS is a browser security feature that controls how websites from different domains (e.g., example.com vs. api.example.com) share resources like images or data. It lets servers whitelist specific domains to access their resources, preventing unauthorized cross-domain requests. Think of it as a passport for data, ensuring safe interactions between websites.

CORS errors can be a headache because browsers store tons of personal data, like cookies, for each site. Without proper CORS restrictions, a sneaky website could hijack your browsing session and potentially steal sensitive information from trusted sites.

The key to solving CORS issues in React and Next.js is to configure your server to accept requests from your front end's origin.

In this article, we will Configure our asp.net web API to do so.

Step 1. Generate an Attribute to handle the Request and pre Process it

In the Generated Class File, add this code snippet.

public class AllowCrossSiteJsonAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        filterContext.RequestContext.HttpContext.Response.AddHeader("Access-Control-Allow-Origin", "*");
        base.OnActionExecuting(filterContext);
    }
}

Step 2. Bind with Action

[AllowCrossSiteJson]
public ActionResult About()
{
DataTable dms = repo.getpro();
string json = JsonConvert.SerializeObject(dms);
return Content(json);
}

In this article, we've tackled the infamous CORS beast, demystifying its intricacies and equipping you with the knowledge to configure your ASP.NET MVC 5 Web API to dance seamlessly with JavaScript frameworks like ReactJS. By implementing the strategies outlined here, you've opened the door for smooth, secure communication between your server-side API and your dynamic client-side applications.

Remember the key takeaways

• Configuring Access-Control Headers: the art of setting the appropriate headers to grant permission for cross-origin requests from the Server side.

Remember, security is paramount. While "AllowAnyOrigin" might seem tempting, consider tailoring your CORS configuration to your specific needs, ensuring only authorized origins can access your precious data.

We hope this article has been a valuable resource in your CORS journey. If you have any questions or challenges, feel free to leave a comment below, and our community will be happy to assist you!