Working with cross-origin requests is an important part of building modern web APIs. If you’re using ASP.NET Core minimal APIs, enabling CORS (Cross-Origin Resource Sharing) can seem tricky at first. But with the right setup, it becomes straightforward to allow your API to communicate with other domains securely.

Getting Started with a New ASP.NET Core Minimal API Project

The first step is to create a new project in Visual Studio. Launch Visual Studio 2022 and select ‘Create a new project.’ From the options, pick ‘ASP.NET Core Web Application’ under the C# templates. Make sure you select ‘.NET 6 (Long-term support)’ for the framework. When choosing the project type, check the ‘API’ box to set up a minimal API project quickly.

Once the project is created, you’ll see a simple setup with minimal files. This is a good foundation to add CORS support. Minimal APIs are lightweight, making it easy to configure middleware like CORS directly in the program file.

Configuring CORS in Your ASP.NET Core Minimal API

To enable cross-origin requests, you need to add CORS middleware to your application’s pipeline. This is done by configuring services in the Program.cs file. You start by calling services.AddCors() inside the builder.Services section. Here, you can define a policy that specifies which origins are allowed to access your API.

For example, you might add a policy called ‘AllowSpecificOrigin’ that permits requests from a particular domain. You do this by setting up the policy with builder.WithOrigins(‘https://example.com’). You can also customize it further by allowing specific headers or methods. After defining the policy, you need to apply it to your API endpoints by calling app.UseCors(‘AllowSpecificOrigin’) before mapping your routes.

Using the CORS middleware is flexible and powerful. It makes it easy to control which external domains can interact with your API. You can also enable CORS on individual endpoints if you prefer more granular control. This is done by decorating your minimal API routes with options to enable CORS, providing an extra layer of security and flexibility.

Alternative Ways to Enable CORS

Besides configuring CORS globally in your Program.cs, you can also enable it on specific endpoints. This is useful if only certain parts of your API need to be accessible from other domains. In minimal APIs, you can chain the .RequireCors() method when defining routes to activate CORS policies selectively.

Another approach is to use attributes like [EnableCors], but this is more common in controller-based APIs. Since minimal APIs are more straightforward, middleware-based setup is usually the best choice. Remember to always specify the correct origins and methods to keep your API secure while allowing necessary cross-origin access.

In summary, setting up CORS in ASP.NET Core minimal APIs involves defining policies in the service container and applying them in the request pipeline. This process helps you control who can access your API from other domains, making your application more flexible and secure. With these steps, you can unlock cross-origin API access easily and confidently.

Inspired by

• https://www.infoworld.com/article/4069660/how-to-use-cors-in-asp-net-core-minimal-apis.html

Sources

• mozilla.org
• microsoft.com
• mozilla.org