How to Use CORS with ASP.NET Core Minimal APIs: A Beginner's Guide
Hi, I'm Jon. Welcome to my blog, where I explain the world of AI and technology in an easy-to-understand way. Today, I'll be talking about how to use a mechanism called CORS (Cross-Origin Resource Sharing) with minimal APIs created using the ASP.NET Core framework. CORS is a set of rules that allow websites and apps to securely exchange data from different domains (e.g., different URLs). I'll explain it step-by-step, starting with the basics, so even beginners can understand it. This article is based on an article published in InfoWorld on October 9, 2025, and has been updated with the latest information.
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What is CORS and why do we need it?
CORS is a mechanism for relaxing the restrictions that browsers impose for security reasons. Normally, when a web page tries to send a request to a server in a different domain, the browser blocks it, saying, "It's not the same domain, so it might be dangerous." This is called the cross-origin problem, but CORS allows you to set permissions on the server side and communicate safely.
For example, CORS is useful when a front-end JavaScript app (e.g., a website built with React) communicates with a back-end API (e.g., a server built with ASP.NET Core). As of 2025, such cross-domain interactions are common in web development, especially in microservices and API-centric applications. According to official Microsoft documentation, ASP.NET Core provides middleware (intermediary processing programs) that make CORS easy to configure.
ASP.NET Core Minimal APIs Basics
First, let's briefly explain Minimal APIs. Minimal APIs is a feature of ASP.NET Core (a web development framework provided by Microsoft) that allows you to create APIs simply. It requires less code than the traditional MVC (Model-View-Controller) pattern, allowing you to create lightweight, fast APIs. A Microsoft Learn tutorial (updated August 21, 2024) describes Minimal APIs as "an approach to building HTTP APIs with a minimum number of files and dependencies."
In the latest ASP.NET Core 9.0 (version as of 2025), the Minimal APIs have been further refined, with enhanced caching and security features. For example, Microsoft's Quick Reference, updated on September 8, 2025, provides a detailed overview of the Minimal APIs, detailing how to easily define routing (URL assignment) and endpoints (API entry points). By incorporating CORS into these Minimal APIs, access from different domains can be permitted.
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Steps to set up CORS with Minimal APIs
Now, let's take a look at how to use it. Based on an InfoWorld article (published on October 9, 2025), I will explain how to configure CORS with ASP.NET Core's Minimal APIs. First, create a project. Set up a Minimal API project using Visual Studio or the command line (dotnet new webapi -minimal).
Next, add the CORS middleware. In your Program.cs file, add the following code:
- builder.Services.AddCors(options => { options.AddPolicy(“AllowAll”, builder => builder.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader()); });
- app.UseCors(“AllowAll”);
This creates a policy called "AllowAll" and sets it to allow requests from all origins (domains). AllowAnyOrigin() allows any domain, AllowAnyMethod() allows all HTTP methods such as GET/POST, and AllowAnyHeader() allows custom headers. However, for security reasons, in actual operations you should limit the allowed domains to specific ones. For example, specify builder.WithOrigins("https://example.com").
Microsoft's CORS documentation (updated September 29, 2025) recommends a policy-based approach to enabling CORS in ASP.NET Core apps, which allows Minimal APIs endpoints (e.g., app.MapGet("/", () => "Hello World");) to accept cross-origin requests.
Latest Updates and Best Practices
As of 2025, ASP.NET Core 9.0 has further enhanced support for CORS. An InfoWorld article details CORS configuration specifically for Minimal APIs, including its use in conjunction with caching. Additionally, Mykola Aleksandrov's blog, published on July 31, 2025, summarizes best practices for CORS configuration when migrating from .NET 8 to 9, from development to production environments.
Looking at recent posts on X (formerly Twitter) (around October 2025), the developer community is talking about the simplicity of Minimal APIs and sharing tips on troubleshooting CORS. For example, if you get a CORS error in your browser console, they advise you to check the server-side policy. However, these posts are personal opinions, so official documentation should take precedence.
As a best practice:
- During development, test using "AllowAnyOrigin", and specify a specific origin in production.
- Don't forget to use AllowAnyMethod to accommodate preflight requests (OPTIONS method).
- For security reasons, be careful when handling credentials (cookies, etc.).
Also, an article published in InfoWorld on September 9, 2025 covers implementing caching and integrating CORS with Minimal APIs, and is full of tips for improving performance.
Summary and Recommendations
Using CORS with ASP.NET Core's Minimal APIs is surprisingly easy. Once you learn the basic settings, cross-domain API communication will be smooth. The latest .NET 9.0 makes these features even easier to use, so be sure to give it a try.
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To sum up, CORS is the foundation of web security, but combining it with lightweight tools like Minimal APIs enables efficient development. Beginners should start with the official tutorial and gradually customize. By keeping up with the latest information, you should be able to consistently create secure apps. I hope this makes your development life more enjoyable!
Reference sources
- InfoWorld: How to use CORS in ASP.NET Core minimal APIs (October 9, 2025) – Article Link
- Microsoft Learn: Tutorial: Create a minimal API with ASP.NET Core (Updated August 21, 2024)
- Microsoft Learn: Enable Cross-Origin Requests (CORS) in ASP.NET Core (Updated September 29, 2025)
- Microsoft Learn: Minimal APIs quick reference (updated September 8, 2025)
- Mykola Aleksandrov's blog: CORS in ASP.NET Core (.NET 8): From Local Dev to Production (July 31, 2025)
- Related posts from X (formerly Twitter) (based on trends around October 2025)