referer（Referrer Policy A Closer Look at HTTP Referer）

摘要：Referrer Policy: A Closer Look at HTTP Referer
The Referrer Policy is an important aspect of web security and privacy. In this article, we will delve into the d

Referrer Policy: A Closer Look at HTTP Referer

The Referrer Policy is an important aspect of web security and privacy. In this article, we will delve into the details of the HTTP Referer header and its implications. By understanding how the Referer header works and the options available to control it, you can better protect the privacy of your users and prevent potential security vulnerabilities.

Understanding the HTTP Referer Header

The HTTP Referer header is an optional header field that contains the URL of the webpage that referred the user to the current page. It is automatically sent by the user's browser to the server when requesting a resource. The Referer header plays a crucial role in a wide range of web applications, including analytics, advertising, and even security mechanisms.

When a user clicks on a link or submits a form, their browser includes the Referer header along with the request. This information allows the server to track the user's navigation path, which can be used for analyzing user behavior, generating statistics, and creating personalized experiences. However, this also means that the URL of the previous page is exposed to the server of the current page.

The Role of Referrer Policy

While the Referer header provides valuable information, it can also pose privacy and security risks. The Referrer Policy is a mechanism that allows website owners to control the information sent by the Referer header and manage the level of exposure of the previous page's URL.

Using the Referrer Policy, website owners can choose to restrict the Referer header to only send the scheme, the domain, or no information at all. This gives them granular control over the data exposed by the Referer header and minimizes the risk of sensitive information leakage. Different policies can be implemented based on the sensitivity of the data being transmitted or the user's preferences.

Available Referrer Policy Options

There are several Referrer Policy options available for website owners to choose from:

1. no-referrer: This policy sends no Referer header, meaning that the previous page's URL is not shared at all. This is the most privacy-oriented option, but it may break some functionality that relies on the Referer header, such as analytics tracking or target-based navigation.
2. no-referrer-when-downgrade: This policy is the default behavior and only sends the Referer header when navigating from an HTTPS page to an HTTP page. It does not send the Referer header when navigating from an HTTPS page to another HTTPS page, from an HTTP page to an HTTPS page, or from an HTTP page to another HTTP page.
3. same-origin: This policy restricts the Referer header to be sent only when the current page has the same origin as the previous page. The origin includes the scheme, domain, and port number. This helps to prevent leaking sensitive information across different origins.
4. strict-origin: This policy is similar to the same-origin policy, but it also omits the path and query string of the URL. It only sends the scheme, domain, and port number of the previous page.
5. strict-origin-when-cross-origin: This policy is the default behavior for cross-origin requests. It includes the full URL of the previous page when the navigation is from a different origin, but it restricts the information to the scheme, domain, and port number when the navigation is from the same origin.
6. unsafe-url: This policy sends the full URL of the previous page, regardless of the origin. It provides the most information to the server, but it also exposes the user's browsing history, including potentially sensitive data.

By choosing an appropriate Referrer Policy, website owners can balance the need for functionality and analytics with the protection of user privacy and security. However, it's important to note that a Referrer Policy is not a foolproof measure and should be used in conjunction with other security practices to ensure a comprehensive approach to web security.

In conclusion, the Referrer Policy plays a significant role in web security and privacy by allowing website owners to control the information exposed by the HTTP Referer header. By understanding how the Referer header works and the available policy options, you can make informed decisions to protect user privacy while maintaining the necessary functionality of your web applications.