Скачать или смотреть Understanding How External Websites Redirect to localhost

Explore how your browser handles redirects from external websites to `localhost`, particularly in `oAuth2` scenarios. Learn about HTTP headers and the redirect process.
---
This video is based on the question https://stackoverflow.com/q/64272935/ asked by the user 'Pankaj Sharma' ( https://stackoverflow.com/u/9140438/ ) and on the answer https://stackoverflow.com/a/64273939/ provided by the user 'Evert' ( https://stackoverflow.com/u/80911/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: how do external website redirects to localhost

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding How External Websites Redirect to localhost

When developing applications, especially those involving OAuth2 services, you might come across a peculiar situation. You provide a callback URL that points to http://localhost:8000/oauth-login. After a successful user login on the external authentication website, it seems to redirect back to your local development server. But how is this possible? Can external websites really redirect to a localhost address that runs on your machine? In this guide, we’ll clarify this process in simple terms.

The Mechanics of Redirects

First off, it’s important to understand that the actual redirecting mechanism is handled by your web browser, not the external website itself. Here’s a breakdown of how this process works:

The Redirect Process

User Authentication:

When you log in to an external service that uses OAuth2, the service authenticates you.

HTTP Response:

Upon successful authentication, the external service sends an HTTP response to the web browser with a redirect instruction.

This response contains a status code (for example, 303 See Other) and a Location header specifying where the browser should go next.

[[See Video to Reveal this Text or Code Snippet]]

Browser Action:

The browser receives this response, interprets the instructions, and then directs you to the specified URL. This is where it gets interesting: the localhost URL points to your local environment rather than a public web server.

Key Points to Remember

Localhost Accessibility: For this redirect to work, you need to have a local server running at the provided localhost address. In our example, that’s where your OAuth2 callback is processed.

No Communication: It’s crucial to note that there’s no active communication between the external website and your local server during this redirection. The server merely instructs the browser to navigate to a URL of its choosing.

Can JavaScript Handle Redirects to Localhost?

In the context of OAuth2 redirects, the process doesn’t involve JavaScript at all. However, JavaScript can be used on your local application to handle the incoming requests once the browser is redirected to localhost. Essentially, you can:

Capture the authentication token sent back from the external service.

Process the user login session locally.

Conclusion

Understanding how external websites can redirect back to your localhost environment is essential for developing and testing OAuth2 applications properly. The key takeaway is that the redirection is managed by your browser based on instructions received from the external server, allowing a seamless transition from the authentication phase back to your local application.

If you're working with OAuth2 and have further questions or comments, feel free to share! Happy coding!