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CORS

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    Bowen Y
    Twitter

What will happen if I allow localhost in CORS policy?

When you allow http://localhost:3000 in your CORS policy, anyone running a frontend on http://localhost:3000 on their own machine will be able to make requests to your backend service. Here's how it works:

  • CORS and Localhost: The http://localhost:3000 you allow in your CORS policy refers to any instance of a service running on port 3000 on localhost. This localhost is specific to the computer that the service is running on.

  • Different People, Different localhost: If multiple people run frontend services on their own localhost:3000, they are running those services on their own machines. Therefore, if your backend service allows requests from http://localhost:3000, it will accept requests from any frontend running at localhost:3000 on any machine.

Key Point:

  • Not Limited to Your Machine: Allowing http://localhost:3000 in CORS does not limit requests to just your machine. It means that any machine with a service running at http://localhost:3000 can make cross-origin requests to your backend service.

    So, if someone else runs a frontend on their own computer at http://localhost:3000, and your backend allows requests from http://localhost:3000, their frontend can access your backend service.

Example:

  • Your Development Setup: You may allow http://localhost:3000 in CORS because your frontend is running locally at localhost:3000 and you want it to communicate with your backend.
  • Another Developer's Setup: Another person on their own computer could also run a frontend at http://localhost:3000. If your backend is publicly accessible and allows requests from http://localhost:3000, their frontend could also make requests to your backend.

Important Considerations:

  • Backend Authentication: While CORS allows cross-origin requests, it doesn't handle authentication. Even if someone can send requests to your backend from http://localhost:3000, your backend should still have proper authentication and authorization mechanisms to control access.
  • Local Development vs. Production: Typically, allowing localhost in CORS is for development purposes. In production, you would restrict CORS to trusted domains (e.g., your deployed frontend's domain) to prevent unintended access.

In summary, allowing http://localhost:3000 in CORS means that anyone running a service on their own localhost:3000 can access your backend, not just you on your own machine.