Elixir CORS

Understanding CORS in Web Development

Cross-Origin Resource Sharing (CORS) is a security feature implemented by web browsers to control how resources can be requested from a different domain than the one that served the initial web page. It is an important aspect of web security because it helps prevent malicious sites from accessing sensitive data from another domain.

In the context of Elixir, handling CORS is crucial for enabling APIs to be accessed from various front-end clients hosted on different domains.

Introduction to Plug.CORS

Plug.CORS is a library in Elixir that provides an easy way to handle CORS requests in your web applications. It is built as a plug, which means it can be integrated into any Elixir web application using the Plug library, especially within the Phoenix framework.

By using Plug.CORS, you can specify which domains are allowed to access your resources, which HTTP methods are permitted, and what headers can be used.

Installing Plug.CORS

First, you need to add Plug.CORS to your project's dependencies. Open the mix.exs file and add the following line to the deps function:

After updating the mix.exs file, run the following command to install the new dependency:

Configuring Plug.CORS

Once installed, you need to configure Plug.CORS in your application. This is typically done in the endpoint.ex file of a Phoenix application. Add the following code snippet to your endpoint configuration:

In this configuration, the CORS plug allows requests from https://example.com, permits the GET and POST methods, and accepts the Authorization and Content-Type headers. The max_age option specifies how long the results of a preflight request can be cached.

Testing Your CORS Configuration

To test your CORS setup, you can use tools like test-cors.org or write a simple HTML page that makes an AJAX request to your server. Ensure that the requests are sent from a different domain than your backend to verify the CORS headers are correctly configured.

Here's an example of a simple JavaScript fetch request:

Conclusion

Implementing CORS in your Elixir application using Plug.CORS is a straightforward process that enhances the security and flexibility of your web services. By managing cross-origin requests, your APIs can safely interact with different clients while maintaining control over who can access your resources.

With this setup, you're now prepared to handle cross-origin requests effectively in your Elixir applications, paving the way for robust and secure API development.