What is UserAgent Client Hints Device Detection on Modern Browsers

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#useragent #clienthints #browsers • What is User-Agent Client Hints? | Device Detection on Modern Browsers • User-Agent request header • A User-Agent (UA) is a string that identifies the ‘agent’(browser) or program making a request to a web server for an asset such as a document, image or web page. • It is a standard part of web architecture and is passed by all web requests in the HTTP headers. • Helps make important decisions on how to handle web traffic. • User-Agent: product / product-version comment • User-Agent: Mozilla/version (system-information) platform (platform-details) • extensions • e.g. • user-agent: • Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.82 Safari/537.36 • Mozilla/5.0 (Linux; Android 5.1.1; Nexus 5 Build/LMY48B; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/43.0.2357.65 Mobile Safari/537.36 • The user agent string can be accessed with JavaScript on the client side using the • navigator.userAgent property. • User-Agent header - Benefits • A browser's user agent string (UA) parsing helps to identify which browser is being used, what version, and on which operating system. • Identify and handle requests from certain types of traffic - load different CSS, Deliver custom JavaScript, different page layouts, different content • Adapt the web site to the specific capabilities of the device • Diagnose browser or device-specific issues such as slow performance of video rendering • Programmatic advertising • Understanding web traffic to improve experiences - analytics. • Fraud and non-human identification services. • Optimizing images and video • User-Agent Header Concerns • With the increasing demand for new attributes, the header size has increased significantly • It also affected user’s privacy since User-Agent transmit all the data to the server by default • Fingerprint users - to identify track individual people without using cookies or other restricted tracking mechanisms • User Agent data is not standard across all the browsers • Complex regex to parse user agent data • User-Agent Client Hints • Client hints were introduced by Google for Chrome, and other browsers have adopted (or in the process of adopting) them since the HTTP specification(https://wicg.github.io/ua-client-hints/) was released. • The User-Agent header freezed in favor of User-Agent Client Hints. • Introduced as an alternative for the User-Agent string allowing access to the same data while protecting the users’ • privacy. • Unlike the User-Agent string, User-Agent Client Hints do not transmit all the data to the server by default. • Reduce the passive fingerprinting surface by locking the User-Agent header and replacing it with a set of opt-in • Client Hints • Client Hints will not be delivered to non-secure endpoints • Server must ask the browser for a set of data about the client (the hints) and the browser applies its own policies or user configuration to determine what data is returned. • Developers also benefit from a simpler API - no more regular expressions • User-Agent Client Hints Header • Request Headers: • Sec-CH-UA : list of browser brands versions (Eg: “Google Chrome”; v=”84 ) • Sec-CH-UA-Platform : Platform for the device, usually the operating system. (Eg: Windows ) • Sec-CH-UA-Platform-Version : Version for the platform or OS. • Sec-CH-UA-Arch : Underlying architecture for the device. (Eg: ARM64) • Sec-CH-UA-Model : The device model. (Eg: “OnePlus 6”) • Sec-CH-UA-Mobile : Boolean indicating if the browser is on a mobile device or not. (?1 for true, ?0 for false) • Sec-CH-UA-Full-Version : The complete version for the browser. (Eg: “73.1.2343B.TR”) • Sec-CH-UA-Bitness - bitness of the architecture of the platform on which a given user agent is executing e.g 64 • Response Headers: • Accept-CH - The Accept-CH header is set by the server to specify which Client Hints headers a client should include in subsequent requests. • Sec-CH-UA and Sec-CH-UA-Mobile are known as low entropy hints, and these 2 hints will be sent by default with the initial request from the client to the server. • If the server needs to know anything other than browser brand and mobile or not, it will have to request it from the client using the Accept-CH header in the response. • Scope of a Hint • Usually, scope of a User-Agent Client Hint is limited to same origin requests. • But if there is a need, we can configure hints in cross-origin requests by specifying Feature-Policy/Permission-Ploicy header. • For example, if you want to get hints from https://example.com to https://sub.example.com , response from https://example.com should include Feature-Policy header in addition to the usual Accept-CH header. • Accept-CH: Sec-CH-UA-Full-Version • Feature-Policy: ch-ua-full-version https://sub.example.com; • Life Time of a Hint - Hints specified via the Accept-CH header will be sent for the duration of the browser session or until a different set of hints are specified.

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