Handling CORS with middleware

CORS is a security feature implemented in web browsers to prevent malicious websites from making unauthorized requests to APIs hosted on different origins. When building APIs, especially for public consumption, it’s crucial to handle CORS properly to ensure legitimate requests are served while unauthorized ones are blocked.

In this recipe, we will explore how to handle CORS using custom middleware in FastAPI. This approach allows us to deeply understand the CORS mechanism and gain flexibility in customizing the behavior to fit specific requirements.

Getting ready

We will apply the recipe to the middleware_project application. Make sure you have the FastAPI application running with at least the GET / endpoint already set up.

Since the recipe will show how to set up CORS middleware to manage CORS, you will need a simple HTML web page that calls our API.

You can create one yourself or download the cors_page.html file from the project...