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Firebase Authentication is a powerful tool for adding user authentication to web apps, but it can be tricky to set up. One common issue that developers encounter is the "unauthorized domain" error, which indicates that the domain you are trying to use Firebase Authentication on is not authorized in the Firebase project's settings.

If you are using Vite as a development server for your project, there are a few additional things to check when encountering the "unauthorized domain" error:

First, verify that your project's development server is correctly configured to proxy requests to the Firebase server. This is typically done in the vite.config.js file, where you may need to specify the proxy URL for your Firebase project.

Next, make sure that your Firebase project's settings allow requests from http://localhost or http://127.0.0.1, as these are the default addresses used by Vite's development server.

Additionally, check if you are using any plugin or package that may be conflicting with Firebase.

Also, make sure that the Firebase SDK is correctly imported and initialized in your code.

If you have already added your domain in the OAuth redirect domains in the Firebase project's settings, double-check that you have entered the correct domain name in the Firebase project's settings and also that your web app is correctly configured to use Firebase Authentication.

In summary, when encountering the "unauthorized domain" error while using Firebase Authentication in a Vite-based project, it's important to check your development server's proxy configuration, ensure that your Firebase project's settings allow requests from the correct domains, and verify that the Firebase SDK is correctly imported and initialized in your code.

Another important step to troubleshoot the "unauthorized domain" error is to double-check that your domain is added to the list of authorized domains in the Firebase project's Authentication settings. Here's how to do it:

• Go to the Firebase console for your project.

• In the left sidebar, click on the "Authentication" option.

• Click on the "Sign-in Method" tab.

• Scroll down to the "Authorized domains" section and add your domain.

• Save the changes.

Whenever you want to run the development server/terminal, make sure you use

`npm run dev -- --host or npm run start -- --host`

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