Cross-site tracking represents one of the most pervasive privacy challenges on the modern web, and the problem becomes particularly acute when users utilize “Login With” services such as “Sign in with Google,” “Login with Facebook,” or similar federated authentication mechanisms that have become ubiquitous across digital platforms. While these services offer tremendous convenience for users who wish to avoid creating yet another unique username and password combination, they simultaneously create sophisticated tracking vectors that allow large technology companies to monitor user behavior across vast networks of unrelated websites. This comprehensive analysis examines the multifaceted challenge of preventing cross-site tracking within federated authentication scenarios, exploring the technical mechanisms that enable tracking, the privacy regulatory frameworks attempting to constrain such practices, the browser technologies designed to block unwanted tracking, and the emerging solutions attempting to balance the legitimate needs of authentication services with robust user privacy protection. Understanding this landscape requires examining the intersection of cookies, OAuth protocols, privacy regulations like the GDPR, browser innovations like Safari’s Intelligent Tracking Prevention, and next-generation authentication approaches such as Federated Credential Management, all while recognizing that the tension between convenience and privacy remains fundamentally unresolved in contemporary internet architecture.
Understanding “Login With” Services and Their Cross-Site Tracking Implications
The explosive adoption of federated identity services—particularly social logins powered by platforms like Facebook, Google, and other large identity providers—has transformed the authentication landscape over the past decade. The appeal is straightforward: rather than requiring users to create unique credentials for every website they visit, federated authentication allows individuals to leverage existing accounts they maintain with major technology companies to gain access to third-party services. From the perspective of users, this represents a significant quality-of-life improvement. Research indicates that approximately eighty percent of users desire website customization and that eighty-six percent of users report frustration at having to create new accounts on websites, making single sign-on solutions genuinely valuable from a user experience perspective. However, this convenience comes with substantial privacy implications that many users neither fully understand nor explicitly consent to experiencing.
When a user clicks a “Sign in with Google” button or similarly branded federated login option, they are initiating a complex authentication flow that involves multiple redirects and information exchanges across different domain boundaries. The technical implementation of these flows, particularly through mechanisms like OAuth 2.0 and OpenID Connect, inherently involves third-party cookies and cross-domain navigation patterns that create opportunities for extensive tracking and user profiling. The fundamental problem is that federated identity providers—the companies managing the authentication infrastructure—can observe which websites and applications a user attempts to access. Every time a user initiates a federated login flow, the identity provider becomes aware of the relying party website being accessed, and this information can be aggregated over time to create a comprehensive profile of the user’s web browsing behavior across otherwise unrelated services.
The scale of this tracking potential is staggering when one considers the market dominance of a handful of identity providers. Google, Facebook, and a few other major platforms control the authentication infrastructure for millions of websites worldwide. This creates a situation where a single company can potentially observe a substantial fraction of a user’s web browsing activity simply by virtue of maintaining the federated identity infrastructure. This data collection is not necessarily nefarious in intent—identity providers argue that understanding which websites their users visit helps them improve their services, detect fraudulent behavior, and optimize their platforms. However, the surveillance implications are profound, and the data being collected about users’ browsing patterns represents genuine personal information about their interests, financial situations, health concerns, and behavioral patterns that could be exploited for targeted manipulation or sold to third parties.
The mechanics of how this tracking occurs involves multiple layers of technology working in concert. First, when a user initiates a federated login, their browser is redirected to the identity provider’s servers to verify their identity. At this stage, the identity provider sets cookies in the user’s browser—specifically, third-party cookies that persist across different website visits. These cookies allow the identity provider to maintain a session with the user and to recognize the user when they return to that provider’s domain in the future, even from different websites. Crucially, if the identity provider’s domain appears as a third-party domain on multiple websites (which it inevitably does, since the same identity provider is used across many relying party websites), the identity provider can use these third-party cookies to track the user across all of those sites through a technique known as cross-site tracking.
Second, beyond the explicit third-party cookies, the redirect flows inherent to many federated authentication implementations create additional tracking opportunities through mechanisms like link decoration. Link decoration involves embedding user-identifying information directly in URLs—for example, including a unique identifier as a URL parameter—that allows trackers to follow users across websites even when cookies are restricted. When a user is redirected from one domain to another through an identity provider’s servers, the URL parameters used in those redirects can contain unique identifiers that link the user’s actions across different websites. Furthermore, the mere fact that a redirect occurred through a particular domain can itself constitute a form of tracking, as the identity provider becomes aware of the navigation pattern.
Third, first-party cookies set by the relying party website can also enable cross-site tracking when the identity provider observes those cookies or when the relying party website shares information about the user’s activities with the identity provider through redirect flows or API calls. The complexity of the authentication flow—involving multiple API calls, data exchanges, and redirect chains—creates numerous opportunities for user identification information to be transmitted across domain boundaries in ways that persist tracking relationships.
How Third-Party Cookies Enable Cross-Site Tracking in Federated Login Scenarios
To comprehensively understand how cross-site tracking occurs within federated authentication contexts, one must examine the specific mechanisms through which third-party cookies function and how browser behavior with these cookies creates tracking vectors. Third-party cookies are cookies set by a domain other than the domain currently displayed in the user’s address bar, and they persist across visits to different websites, enabling the cookie-setting domain to track user behavior across multiple unrelated sites. The distinction between first-party and third-party cookies is fundamental to understanding web tracking. First-party cookies, set by the website the user is directly visiting, serve legitimate purposes such as maintaining login sessions, remembering user preferences, and implementing security features. Third-party cookies, by contrast, are primarily used for cross-site tracking by advertisers, analytics providers, and identity management systems.
In the context of federated authentication, the identity provider (such as Google) sets third-party cookies when users attempt to log in through the provider’s infrastructure. These cookies contain session identifiers that allow the identity provider to maintain state across the authentication flow and, critically, across multiple unrelated websites where the user subsequently attempts to use federated login features. Because the identity provider’s domain appears as a third-party domain on any website using that provider’s login services, the identity provider can leverage these persistent cookies to track when users visit those websites, even if the users do not actually complete the login process at each visit.
The technical implementation involves what security researchers call the “Storage Access API” problem, though the mechanism existed before this API was formally defined. When a user is redirected to an identity provider’s login page to authenticate, the browser allows the identity provider to set cookies from its own domain, even though the identity provider technically operates as a third party relative to the website where the user initiated the login request. Once the user completes authentication and is redirected back to the relying party website, the identity provider’s domain has successfully set a session cookie that persists across multiple visits to different websites. Subsequent visits to other websites using the same identity provider will cause the user’s browser to send that persistent cookie back to the identity provider’s servers, allowing the identity provider to recognize the returning user and correlate their activities across websites.
The problem becomes more sophisticated when considering how identity providers can leverage cross-domain data collection. Identity providers operate not just as authentication services but as comprehensive data collection platforms with presence across the web through analytics services, advertising networks, and embedded social widgets. Google’s vast infrastructure—comprising Google Analytics, Google Ads, Google Sign-In, and other embedded services—creates multiple opportunities for Google to observe user behavior across websites, regardless of whether users are explicitly logging in with their Google accounts. Facebook similarly maintains numerous tracking mechanisms beyond its core social network, including the Facebook Pixel embedded on millions of e-commerce sites, which allows Facebook to track user behavior even on websites where users never explicitly authenticate through Facebook.
The persistence of these cookies exacerbates the tracking problem. Unlike session cookies that expire when the browser is closed, many authentication-related cookies set by identity providers persist across browsing sessions, sometimes for extended periods. The GDPR and similar privacy regulations require explicit user consent before setting cookies beyond strictly necessary ones, yet many identity providers maintain that authentication-related cookies fall within the category of “strictly necessary” cookies exempt from consent requirements. This classification is legally and technically debatable, as users could theoretically authenticate without maintaining persistent tracking cookies, yet the practice of setting long-lived cookies by identity providers remains widespread.
Furthermore, the interaction between federated authentication cookies and other tracking mechanisms creates compounding privacy risks. Identity providers often employ techniques like bounce tracking, in which a user is rapidly redirected through the identity provider’s domain for tracking purposes, and then redirected back to the original website. These bounce redirects allow identity providers to observe the referring website without the identity provider’s domain appearing in any obvious way on the user’s screen. The browser sees multiple navigations, but from the user’s perspective, they simply experienced a momentary pause during the authentication process. During these brief redirects, the identity provider can set or read cookies, observe referrer information indicating which website the user came from, and correlate this information with other observations of the user’s activities.
Browser-Based Tracking Prevention Mechanisms and Their Limitations
Recognizing the pervasive privacy threats posed by cross-site tracking, major web browsers have implemented increasingly sophisticated tracking prevention technologies designed to limit how identity providers and advertisers can monitor user behavior across the web. These mechanisms represent a crucial infrastructure for privacy protection, yet they simultaneously create technical challenges for legitimate federated authentication use cases. Understanding these browser protections is essential for comprehending both the progress that has been made in privacy protection and the ongoing limitations that persist despite these innovations.
Safari’s Intelligent Tracking Prevention (ITP) represents one of the earliest and most aggressive implementations of browser-level tracking prevention. Implemented across all Safari browsers on both macOS and iOS, ITP uses a combination of machine learning and privacy-focused cookie restrictions to identify and block cross-site trackers. ITP operates on multiple levels. First, it blocks third-party cookies entirely by default, with limited exceptions that require explicit user interaction and verification that the user has actually engaged with content from the third-party domain. Second, Safari categorizes websites into tracking and non-tracking categories based on their apparent engagement in cross-site tracking behaviors, using heuristics that analyze domains’ data collection practices. Third, ITP imposes strict time limits on first-party cookies that appear to be used for cross-site tracking purposes, particularly cookies set via link decoration (where URLs contain tracking parameters)—such cookies expire within twenty-four hours unless the user actively engages with the website.
These Safari protections create significant complications for federated authentication scenarios. When Safari detects that a website is using federated login services, the browser’s Enhanced Tracking Protection can inadvertently block necessary authentication flows, as the redirects through identity provider domains may trigger ITP’s blocking mechanisms. Users of Safari may experience situations where federated authentication fails entirely with confusing error messages, as the browser’s privacy protections interfere with the authentication process. This represents a genuine technical conflict between privacy protection and functionality—Safari’s protections are explicitly designed to prevent the cross-site tracking that federated authentication inherently involves, yet federated authentication represents a legitimate use case that many websites and users depend upon.
Firefox’s Enhanced Tracking Protection (ETP) takes a somewhat different approach to privacy protection, operating primarily through blocklist-based classification of known trackers rather than behavioral heuristics. Firefox offers users three levels of protection: Standard (the default), Strict, and Custom, with each level implementing increasingly aggressive tracking prevention. In Standard mode, Firefox blocks third-party cookies from known trackers and prevents known fingerprinting scripts from executing, while maintaining broader compatibility with websites. In Strict mode, Firefox blocks third-party cookies from all sources except those the user has explicitly whitelisted, achieving more comprehensive privacy protection at the cost of potentially breaking functionality on some websites.
Firefox’s approach to managing the conflict between tracking prevention and authentication functionality involves using the Storage Access API, a web standard that allows third-party content (such as identity provider login forms embedded in iframes) to request permission to access third-party cookies. When a user interacts with a login form from an identity provider, the Storage Access API can enable that form to access third-party cookies it would normally be blocked from accessing, allowing the authentication flow to complete successfully. However, the Storage Access API requires either explicit user interaction or, in some cases, prior user visits to the third-party domain, which can create friction in authentication workflows, particularly for users who have never previously visited the identity provider’s main website directly.
Microsoft Edge implements tracking prevention that aligns broadly with the approach used in Chromium-based browsers, offering users three levels of protection: Basic, Balanced (the default), and Strict. Like Firefox, Edge primarily uses blocklists of known trackers rather than behavioral analysis, though Edge also incorporates metrics about user engagement with websites to determine whether to apply tracking protections. Edge’s approach is more permissive toward cross-site functionality than Safari’s in many cases, particularly for organizations that operate multiple related domains or have established user engagement with the sites attempting to access their cookies.
Google Chrome’s approach to tracking prevention represents a particularly complex landscape. As the browser controlled by Google—a company that derives substantial revenue from advertising and data collection—Chrome’s tracking prevention policies face inherent tensions between user privacy and the business interests of the platform itself. Chrome has gradually implemented restrictions on third-party cookies, with Google announcing that third-party cookies would eventually be removed entirely, though the timeline for this transition has been repeatedly delayed. In the interim, Chrome offers users basic tracking prevention by default, though not as aggressive as Safari’s protections.
However, Chrome’s development of the Privacy Sandbox initiative—a comprehensive approach to maintaining certain online advertising and targeting capabilities while restricting traditional tracking cookies—raises additional privacy concerns. The Privacy Sandbox includes proposals like Federated Learning of Cohorts (FLoC), which was designed to group users into cohorts based on their browsing history for targeted advertising purposes, though FLoC was ultimately discontinued after significant privacy criticism. The Privacy Sandbox continues to evolve with alternative proposals like the Topics API, though critics argue these alternatives still enable sophisticated tracking capabilities while concentrating data access power in Google’s hands.
The fundamental limitation of all browser-based tracking prevention is that these technologies must navigate a delicate balance between privacy protection and maintaining web functionality. Many legitimate services—including federated authentication, embedded payment processors, and cross-domain analytics—rely on cookies and cross-domain requests that tracking prevention technologies can inadvertently interfere with. Browsers have attempted to address this through allowing certain exceptions for authenticated relationships, but determining which relationships are legitimate versus surveillance-oriented remains technically challenging.
Furthermore, determined trackers continue to develop circumvention techniques that sidestep browser protections. Bounce tracking, link decoration, and increasingly sophisticated fingerprinting techniques continue to enable cross-site tracking even as browsers implement restrictions on cookies. Device fingerprinting—the collection of information about a user’s device hardware and software configuration to create a unique identifier—represents a particularly troubling tracking vector that many browser protections do not adequately address. While Firefox and Safari have implemented protections against fingerprinting by limiting the information websites can access about device characteristics, the mechanisms for fingerprinting remain multifaceted and partially mitigable.
Privacy and Regulatory Frameworks Governing Federated Authentication and Cross-Site Tracking
The privacy concerns raised by cross-site tracking in federated authentication contexts have prompted regulatory interventions, most notably the European Union’s General Data Protection Regulation (GDPR), which fundamentally transformed how organizations can collect and process personal data. Understanding the GDPR’s requirements, along with similar regulations emerging globally, is essential for comprehending both the legal obligations that federated authentication services must satisfy and the user protections that these regulations attempt to establish.
The GDPR’s foundational principle is that personal data should only be collected and processed when organizations have established a lawful basis for processing and have obtained explicit consent from data subjects for non-essential processing. For federated authentication services, the GDPR creates several specific requirements. First, identity providers must establish that they have a lawful basis for collecting information about which websites users visit through federated authentication. The GDPR lists several potential lawful bases, including contractual necessity (if the processing is necessary to fulfill a service the user has requested), legitimate interests (if the organization has a genuine business reason for processing that outweighs the user’s privacy interests), or explicit consent.
Most identity providers attempt to justify cross-site tracking by claiming either contractual necessity (arguing that observing authentication patterns is necessary to provide authentication services) or legitimate interests (arguing that detecting fraudulent authentication attempts or improving authentication services justifies monitoring patterns). However, the GDPR’s legitimate interests balancing test requires organizations to weigh their business interests against users’ privacy expectations and potential harms. The EDPB (European Data Protection Board), which provides guidance on GDPR interpretation, has increasingly scrutinized whether cross-site tracking can genuinely satisfy the legitimate interests basis. Furthermore, the GDPR’s transparency requirements mandate that organizations explicitly disclose what data they collect, how they use it, and with whom they share it—requirements that many federated authentication implementations arguably fail to satisfy adequately, as users clicking “Sign in with Google” frequently do not receive clear information about the extent to which their browsing activities will be monitored.
The GDPR also mandates that users have control over their personal data and can withdraw consent at any time. For federated authentication, this creates obligations for identity providers to enable users to understand what tracking has occurred and to delete or restrict processing of cross-site tracking data upon user request. Many identity providers provide limited controls for users to access this information, and users often lack practical mechanisms to understand or restrict the extent of cross-site tracking occurring through federated authentication flows.
Beyond the GDPR, other regulatory frameworks are emerging to address cross-site tracking and digital privacy more broadly. California’s California Consumer Privacy Act (CCPA) and the subsequent California Privacy Rights Act (CPRA) establish consumer rights regarding personal information collection, including rights to know what data is collected, rights to delete collected data, and rights to opt out of certain data processing activities. While less prescriptive than the GDPR about specific mechanisms like cookies, these California regulations create obligations for organizations engaged in digital tracking to provide transparency and user control mechanisms.
The ePrivacy Directive, which operates alongside and complements the GDPR in the European Union, provides additional specific requirements regarding cookies. The Directive mandates that websites obtain prior consent before storing information on users’ devices through cookies, with exceptions only for strictly necessary cookies used for authentication or security purposes. This requirement has generated substantial legal uncertainty regarding federated authentication cookies—are identity provider cookies strictly necessary for authentication, or do they constitute optional tracking that requires explicit consent? This ambiguity has led to inconsistent implementation across organizations, with some treating identity provider cookies as strictly necessary and not requiring consent, while others seek explicit consent before setting federated authentication cookies.
These regulatory frameworks have driven significant changes in how federated authentication services operate, particularly in Europe. Many organizations have implemented consent management platforms designed to obtain explicit user consent for non-essential cookies, including those set by identity providers for authentication purposes. However, consent management has itself become controversial, as research indicates that users frequently do not carefully read consent notices and may grant permissions they would not explicitly choose if given clearer information about the implications.
Beyond formal legal regulations, industry standards and best practice frameworks have emerged to address privacy concerns in federated authentication. The OAuth 2.0 Security Best Practices and similar RFC proposals have established technical recommendations designed to improve the security and privacy properties of federated authentication implementations. However, compliance with these recommendations remains voluntary and inconsistent across the industry.
Technological Solutions for Privacy-Preserving Federated Authentication
Recognizing the tension between the privacy threats posed by traditional federated authentication and the legitimate needs for cross-platform identity management, the web standards community and major browser vendors have developed alternative approaches designed to enable federated authentication while substantially reducing cross-site tracking capabilities. The most significant of these emerging solutions include Federated Credential Management (FedCM), the Storage Access API, Cookies Having Independent Partitioned State (CHIPS), and Related Website Sets, each representing different technical approaches to balancing privacy and functionality.
Federated Credential Management (FedCM) represents a fundamental reimagining of how federated authentication should operate in a privacy-conscious internet. Rather than relying on iframes, redirects, and third-party cookies to enable authentication, FedCM proposes a browser-mediated authentication flow that provides the federated login capability users expect while preventing the identity provider from directly observing which website the user is attempting to access. Under FedCM, when a user clicks a “Sign in with Identity Provider” button, the browser mediates the authentication process instead of allowing the identity provider to directly observe the relying party website.
The technical implementation involves several key components. First, the identity provider must implement specific FedCM endpoints that the browser can query to determine what accounts the user has with that identity provider. Second, the browser controls the presentation of the login UI, rather than allowing the identity provider to control how the login appears. Third, the browser obtains authentication credentials from the identity provider without revealing to the identity provider which specific website the user is attempting to access. Fourth, the browser passes the authentication credential to the relying party website without allowing the identity provider to observe this transmission. This architecture fundamentally prevents the identity provider from using the federated authentication infrastructure for cross-site tracking, as the identity provider cannot directly observe which websites users are attempting to access through the federated login mechanism.
FedCM support is currently limited but growing, with support now available in Chrome and some other Chromium-based browsers, though Safari and Firefox have been slower to implement FedCM. The slower adoption reflects both technical complexity and some concerns within the browser community about whether FedCM adequately addresses all federated authentication use cases. However, Google, the primary proponent of FedCM, has begun migrating its federated authentication services to FedCM, suggesting that at least this major identity provider is committed to privacy-preserving approaches to federated authentication.
The Storage Access API provides a different approach to privacy-preserving cross-domain functionality. Rather than completely preventing identity providers from accessing third-party cookies, the Storage Access API allows embedded content (such as a login form from an identity provider displayed in an iframe on a relying party website) to explicitly request access to third-party cookies. If the user grants permission, the embedded identity provider content can access cookies it would otherwise be blocked from accessing. The critical distinction is that the user must actively grant permission, and the permission is granted per-frame—meaning that each individual embedding of identity provider content must separately obtain permission.
The Storage Access API has been implemented across all major browsers, though the specific mechanics vary somewhat between browser implementations. In Safari, the Storage Access API causes the browser to display a prompt asking the user whether they wish to allow the identity provider to access their stored data. In Firefox, the browser only prompts after an origin has requested storage access on more than a threshold number of websites, reducing prompt fatigue while still providing user control. In Chrome, the browser displays prompts for embedded content that has not previously received storage access. The advantage of this approach is that it maintains backward compatibility with existing federated authentication implementations while gradually introducing user control and transparency about when third-party storage access occurs.
Cookies Having Independent Partitioned State (CHIPS) addresses a specific limitation of preventing third-party cookies: some legitimate services genuinely need to maintain state across multiple websites, including certain federated authentication scenarios and embedded services like chat widgets or maps. CHIPS allows third parties to opt into “partitioned” cookie storage, where cookies set with the Partitioned attribute are stored in separate cookie jars for each top-level website. This means that when a third-party service sets a partitioned cookie while embedded on website A, that cookie is only accessible when the same third party is embedded on website A—the cookie cannot be used to track the user when the third party appears on website B. CHIPS maintains some functionality for cross-domain services while preventing the cross-site tracking that traditional third-party cookies enable.
Related Website Sets (formerly known as First-Party Sets) provide another mechanism for privacy-preserving cross-domain functionality. Related Website Sets allow organizations that operate multiple related domains to declare these relationships to the browser, enabling limited unpartitioned cookie access between the related domains while maintaining restrictions against unrelated cross-site tracking. For example, if an organization operates both www.example.com and accounts.example.com as clearly related services, the organization can declare these domains as a related website set, allowing these domains to share cookies while still maintaining restrictions against cross-site tracking to unrelated third-party domains.
These technological solutions represent genuine progress toward privacy-preserving authentication. However, each solution involves tradeoffs and limitations. FedCM requires substantial changes to how identity providers implement authentication services and currently lacks universal browser support. The Storage Access API, while more compatible with existing implementations, still requires users to understand and make decisions about storage access, placing cognitive burden on users who may not comprehend the privacy implications. CHIPS prevents cross-site tracking but also limits some legitimate cross-domain functionality. Related Website Sets only apply to genuinely related domains, not to unrelated third-party services.
Practical Challenges and Ongoing Conflicts Between Authentication Functionality and Privacy Protection
Despite the progress represented by browser tracking prevention technologies and privacy-preserving federated authentication standards, substantial practical challenges remain in balancing the functionality that users and organizations depend upon with the privacy protections that users increasingly expect and that regulations increasingly mandate. These challenges manifest at multiple levels: technical challenges in implementing privacy-preserving authentication that maintains backward compatibility, business incentives that encourage more extensive tracking rather than less, and user experience challenges in communicating privacy implications without overwhelming users with technical details.
The technical challenges are particularly acute for organizations that have invested heavily in traditional federated authentication implementations relying on OAuth flows, redirects, and third-party cookies. Migrating to FedCM or other privacy-preserving approaches requires substantial development effort and coordination between identity providers and relying party websites. For smaller organizations or those with legacy systems, this migration represents significant technical and financial burdens. Furthermore, some federated authentication use cases—such as enabling federated single sign-on across multiple applications within an organization, or enabling certain advanced authentication scenarios—may not be fully supported by emerging privacy-preserving standards.
The business incentives challenging privacy protection in authentication contexts arise from the fact that federated authentication providers benefit enormously from cross-site tracking capabilities. For identity providers like Google and Facebook that derive substantial revenue from advertising, the data collected about users’ web browsing habits through federated authentication infrastructure represents genuinely valuable business assets. Cross-site tracking enables these companies to refine user targeting for advertising, understand user interests and behaviors more comprehensively, and maintain competitive advantages in the digital advertising market. The financial incentives to maintain cross-site tracking capabilities are therefore substantial and structural, potentially exceeding the incentives to adopt privacy-preserving approaches that would eliminate this valuable data source.
User experience challenges emerge when privacy protections require users to make decisions or understand complex technical scenarios. For example, when Safari or Firefox displays a prompt asking whether the user wishes to allow cross-site tracking, many users lack the context to make an informed decision. They may simply click “Allow” without understanding the implications, or they may be confused about why the browser is asking permission for something they view as fundamental functionality (logging in to a website). The challenge of communicating privacy implications in ways that users can meaningfully understand remains largely unsolved across the industry.
Additionally, the fragmented browser landscape creates implementation challenges for organizations seeking to support privacy-preserving authentication while maintaining compatibility across browsers with different tracking prevention mechanisms. Websites may need to implement multiple authentication pathways—using FedCM where available, falling back to Storage Access API requests in other browsers, potentially maintaining traditional OAuth flows for older browser versions, and potentially even requiring users to supply email addresses as alternative authentication methods when federated authentication fails due to tracking prevention.
A particularly troubling scenario emerges when browser tracking prevention interferes with legitimate authentication functionality, creating frustrating user experiences that may ultimately drive users toward less private authentication methods or cause users to simply abandon websites that fail to authenticate them properly. For example, a user attempting to log into a website using Safari with strict tracking prevention might encounter an authentication failure, forcing them to either disable Safari’s privacy protections temporarily (reducing their overall privacy across all browsing), create a local account on the website (trading the simplicity of federated login for maintaining yet another password), or simply leave the website and seek an alternative. These scenarios represent genuine conflicts between privacy protection mechanisms and usability.
The problem of authentication failures due to tracking prevention is not merely hypothetical. Research and support forums document cases where Safari’s Intelligent Tracking Prevention interferes with federated authentication using username and password flows, where users are unable to complete authentication when using strict tracking prevention settings, and where the relationship between cross-site tracking prevention and authentication functionality remains unclear to end users. Organizations have developed workarounds such as popup-based authentication flows that establish a first-party context for authentication before redirecting back to the original website, but these workarounds often feel clunky and reduce the seamlessness that federated authentication is supposed to provide.
Best Practices for Organizations and Users in Managing Cross-Site Tracking Related to Federated Authentication
Given the complexity of the landscape—involving privacy regulations, browser protections, technical standards, and business incentives—both organizations operating federated authentication services and individual users navigating authentication scenarios can benefit from understanding best practices for managing cross-site tracking risks while maintaining functional authentication experiences.
For organizations implementing federated authentication services, the foundational best practice involves adopting a privacy-by-design approach that minimizes cross-site tracking from the outset rather than treating privacy as an afterthought. This means evaluating whether federated authentication implementations genuinely require extensive cross-site tracking capabilities or whether tracking can be substantially limited while maintaining authentication and security functionality. Identity providers should carefully assess which user data is genuinely necessary for providing authentication services versus which data collection serves primarily to enable additional surveillance or data monetization.
Organizations should implement robust consent management systems that clearly explain to users what data will be collected through federated authentication, why such collection occurs, and what users’ options are regarding this data collection. Rather than seeking vague, general consent or relying on implicit consent through user actions, organizations should strive to obtain explicit, informed consent from users who understand the specific implications of cross-site tracking through federated authentication. This requires moving beyond generic privacy policies and implementing clear, specific disclosures about federated authentication data collection practices.
Technical best practices include adopting emerging privacy-preserving standards such as FedCM where feasible, implementing the Storage Access API to enable user control over cross-domain storage access, and utilizing CHIPS for third-party services that genuinely require cross-domain functionality while preventing cross-site tracking. Organizations should also implement strong security measures to protect authentication credentials and tokens, including using short-lived access tokens with refresh token rotation, implementing PKCE (Proof Key for Code Exchange) for all OAuth implementations, and validating authorization code legitimacy to prevent various OAuth attack vectors.
Additionally, organizations should maintain transparent communications with users about how they can access and manage their authentication-related data, withdraw consent for non-essential data collection, and understand what information about their web browsing activities may be inferred from their use of federated authentication. Organizations should also monitor regulatory developments and industry standards to ensure their implementations remain aligned with evolving legal and technical requirements as regulations like GDPR continue to mature and as technical standards like FedCM mature and achieve broader adoption.
For users attempting to navigate federated authentication while protecting their privacy, several practical strategies can meaningfully reduce cross-site tracking while maintaining functional authentication. First, users should carefully evaluate their privacy preferences and adjust browser settings to reflect those preferences. For Safari users, enabling “Prevent Cross-Site Tracking” in Safari Settings, or using even stricter “Strict” mode for Intelligent Tracking Prevention, substantially reduces cross-site tracking from federated authentication services. Firefox users should enable “Strict” mode for Enhanced Tracking Protection and consider using Firefox’s Private Browsing mode for sensitive activities. Chrome users should enable blocking of third-party cookies in privacy settings, though Chrome’s protections remain less comprehensive than Safari or Firefox.
Second, users should carefully review the information shared when enabling federated authentication. Most identity providers and relying party websites display permissions dialogs indicating what information will be shared through the federated authentication. Users should review this information before granting permission and should only enable permissions for information genuinely necessary for the service being accessed. Users should be particularly cautious about granting permissions for email addresses, friend lists, or profile information unless such information is clearly necessary for the service.
Third, users can reduce federated authentication-driven tracking by limiting their use of federated authentication only to services where they have legitimate reasons to use it, and by maintaining local credentials on websites where doing so does not impose excessive burdens. While this creates the password management challenge that federated authentication was designed to solve, users concerned about cross-site tracking should recognize that the convenience of federated authentication comes at the cost of enabling potentially extensive tracking.
Fourth, users should use privacy-enhancing tools beyond browser built-in protections. Virtual Private Networks (VPNs) can encrypt internet traffic and obscure IP addresses, making it more difficult for identity providers to correlate user activities across websites even if cookies are used. Cookie blockers and tracker blockers provide additional layers of protection beyond browser built-in tracking prevention. However, users should recognize that these supplementary tools cannot entirely eliminate tracking vectors inherent to federated authentication, as the authentication protocols themselves necessarily involve the identity provider observing certain aspects of user behavior.
Fifth, users should understand and utilize the tools available to them for accessing and controlling the information about their activities maintained by identity providers. Most major identity providers maintain user data portals where users can view data collected about them and in some cases manage data retention and deletion preferences. Users should periodically review this data and exercise their rights regarding data deletion and restriction of processing where available under applicable privacy regulations.
Emerging Developments and Future Directions in Privacy-Preserving Authentication
The landscape of federated authentication and cross-site tracking prevention continues to evolve, with multiple promising developments emerging that may substantially improve privacy outcomes in coming years. Understanding these emerging approaches is important for appreciating the trajectory of this technological and regulatory domain.
Google’s Privacy Sandbox initiative represents Google’s most ambitious effort to simultaneously reduce cross-site tracking while preserving certain online functionality including federated authentication and targeted advertising. Beyond FedCM, the Privacy Sandbox includes proposals like Attribution Reporting APIs designed to enable measurement of advertising effectiveness without tracking individual users, Shared Storage APIs designed to enable some cross-site functionality without exposing individual user identifiers, and bounce tracking mitigations designed to prevent tracking through redirect chains. While Privacy Sandbox proposals have generated significant criticism regarding whether they genuinely protect privacy or merely concentrate power in Google’s hands, these efforts represent substantial investment in the technical problem of maintaining certain web functionality while reducing cross-site tracking.
Decentralized authentication approaches represent a more radical reimagining of federated authentication that could potentially eliminate cross-site tracking entirely by removing the need for centralized identity providers to maintain comprehensive information about user authentication activities. Decentralized authentication mechanisms leveraging blockchain technology or similar distributed ledger systems would enable users to prove their identity and authorization without relying on centralized services to observe and track authentication patterns. However, decentralized authentication remains largely in research and early implementation phases, faces significant scalability challenges, and remains unclear whether sufficiently practical decentralized solutions can achieve the convenience and simplicity that centralized federated authentication provides.
Passwordless authentication approaches, including biometric authentication and hardware security keys, represent another direction that could potentially reduce the surveillance implications of traditional federated authentication by enabling authentication without reliance on password-based identity providers. If biometric or hardware key-based authentication became sufficiently widespread and convenient, users might rely less heavily on federated authentication from large identity providers, potentially reducing the cross-site tracking opportunities available to those providers. However, this scenario requires substantial changes to authentication infrastructure across the internet, increased adoption of hardware security keys or biometric devices, and development of robust standards for non-centralized biometric authentication and hardware key authentication.
The regulatory environment continues to evolve in ways that may drive further privacy protections in federated authentication. As regulators like the EDPB provide more specific guidance on GDPR compliance for cross-site tracking through federated authentication, and as additional jurisdictions implement privacy regulations comparable to GDPR, the legal costs of maintaining privacy-invasive federated authentication may increase sufficiently to drive more organizations toward privacy-preserving approaches.
Solidifying Your Login Privacy
The challenge of preventing cross-site tracking in the context of federated authentication represents one of the most consequential tensions in contemporary internet privacy. On one hand, federated authentication through services like “Sign in with Google” or “Login with Facebook” offers genuine, substantial value to users by reducing password fatigue, simplifying account creation, and enabling seamless authentication experiences across the web. Research demonstrates that approximately eighty percent of users desire personalized website experiences and that authentication friction represents a genuine usability obstacle for many internet users. From this perspective, federated authentication represents a successful internet technology that has substantially improved user experience.
On the other hand, federated authentication inherently enables identity providers to observe users’ web browsing patterns across vast networks of unrelated websites, creating surveillance capabilities that enable targeted manipulation, discriminatory practices, and privacy violations at scales that would have been unimaginable in pre-internet contexts. The data collected about users’ browsing behaviors through federated authentication can reveal intimate details about users’ health concerns, financial situations, political beliefs, relationship statuses, and countless other aspects of their lives. This data can be and is sold to third parties, used to train manipulative algorithmic systems, and leveraged to enable behaviors ranging from targeted advertising to discriminatory lending practices.
Addressing this tension requires simultaneous progress across multiple domains. Regulatory frameworks like the GDPR have begun establishing legal obligations for privacy protection and user control, though the effectiveness of these regulations remains mixed, and compliance remains inconsistent across the industry. Browser-level tracking prevention mechanisms have substantially improved, with Safari, Firefox, and other browsers implementing sophisticated protections that meaningfully reduce cross-site tracking—yet these protections remain incomplete and can sometimes interfere with legitimate functionality. Privacy-preserving technical standards like FedCM represent genuine progress toward enabling federated authentication without enabling cross-site tracking, though adoption remains limited and significant technical challenges remain.
Most fundamentally, resolving the tension between federated authentication and cross-site tracking protection requires acknowledging that these two objectives—seamless authentication and comprehensive privacy protection—cannot be perfectly harmonized. Instead, society must collectively make tradeoff decisions about how much privacy protection to prioritize relative to authentication convenience. These decisions manifests through regulatory choices about what data collection is permissible, through browser design choices about what tracking prevention mechanisms to implement and how aggressively to enforce them, through organizational decisions about what federated authentication practices to adopt, and through user choices about how to balance authentication convenience against privacy concerns.
The evidence suggests that current implementation of federated authentication privileges convenience over privacy in ways that many users would reject if given more genuine choices and clearer information. Surveys consistently show that substantial majorities of users express strong privacy preferences and indicate that they would reject cross-site tracking if offered meaningful alternatives. This suggests that the current equilibrium overweights convenience relative to user preferences regarding privacy. Moving toward outcomes more aligned with user preferences requires both continuing to advance privacy-protecting technologies like FedCM and pursuing regulatory approaches that establish clearer legal foundations for user privacy in federated authentication contexts.
The ongoing development of privacy-preserving authentication technologies, coupled with evolving regulatory frameworks and increasing user awareness of privacy issues, suggests that the landscape of federated authentication will continue to evolve toward somewhat greater privacy protection in coming years. Organizations implementing federated authentication should begin adopting privacy-preserving standards like FedCM where feasible, implementing transparent consent systems, and recognizing that users’ privacy preferences are increasingly a legitimate constraint on how extensively they can monitor user behavior through authentication infrastructure. Users concerned about cross-site tracking should actively configure browser privacy settings, exercise available controls over data collection by identity providers, and carefully evaluate whether the convenience of federated authentication justifies the privacy costs in their specific circumstances.
Ultimately, preventing cross-site tracking related to federated authentication is not primarily a technical problem to be solved through browser innovations or clever engineering—though these technical approaches remain valuable and necessary. Rather, it is fundamentally a question about what kind of internet society chooses to build: an internet where seamless convenience and extensive personalization are enabled through comprehensive surveillance of user behavior, or an internet where authentication can occur reliably while limiting organizations’ ability to observe users’ behavioral patterns across the web. Achieving meaningful progress toward the latter vision requires sustained commitment from regulators, technology companies, and users themselves to prioritize privacy alongside convenience in the authentication infrastructure that has become fundamental to contemporary internet access.
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