Managing Third-Party Cookie Deprecation in Android TWAs

The web platform is undergoing a fundamental shift as browsers phase out support for third-party cookies to improve user privacy. Because Trusted Web Activities (TWAs) are powered directly by Chrome Custom Tabs, they share the underlying browser engine, security parameters, and cookie storage policies of the system-installed Google Chrome. Consequently, changes to Chrome cookie handling directly impact how your wrapped Android application behaves.

For many SaaS platforms, ecommerce applications, and multi-tenant tools, third-party cookies have historically been used to handle authentication across subdomains, load embedded widgets, or track user states across different integrated platforms. If your TWA relies on cross-site resources, understanding how to navigate this deprecation is critical to preventing broken user sessions, broken checkout flows, and authentication errors.

How the Deprecation Affects TWA Applications

In a standard web environment, a third-party cookie is any cookie written by a domain different from the domain displayed in the browser URL bar. In an Android TWA, the root domain of your application is defined by your Start URL in the Web App Manifest and verified through Digital Asset Links.

If your TWA attempts to load resources, iframes, or script targets from another domain, any cookies attached to those requests are treated as third-party. Common areas where this creates points of failure include:

• Federated Authentication: Relying on external identity providers that use cookies inside an iframe to maintain login state.
• Embedded Payment Gateways: Using legacy web-based checkout flows nested within an iframe that expect to read session cookies.
• Cross-Domain Content Delivery: Accessing customer data, preferences, or media assets hosted across distinct domain architectures without explicit modern storage permissions.

If these scenarios apply to your architecture, your users will experience unexpected logouts, missing shopping carts, or broken features as Google Chrome systematically blocks these cookie transmissions.

The Shared Cookie Jar in TWAs

Unlike WebView-based applications which operate in isolated sandbox containers with independent cookie policies, TWAs utilise a shared cookie jar with Chrome. This architecture has substantial benefits: if a user is logged into your service on Chrome, they are often automatically logged into your installed Android app as well.

However, this shared nature means that Chrome global security settings apply universally. When a user or Google Chrome defaults to blocking third-party cookies globally, those restrictions instantly apply inside your TWA. This behaviour can make debugging difficult, as developers testing on emulators with default configurations may miss issues that appear for real users who have stricter privacy settings enabled on their personal handsets.

Diagnosing Cookie Issues Inside Your TWA

Before implementing code changes, you must identify where third-party cookies are being utilized inside your application. You can do this by inspecting your TWA using Chrome Developer Tools via USB debugging on a physical device or emulator.

Once connected, navigate to the Application panel in Developer Tools, locate the Cookies dropdown, and review the domains listed. Any entry that does not match your primary application domain is potentially vulnerable. Additionally, the Chrome Console will display explicit warnings for cookies that lack modern parameters or are blocked due to cross-site restrictions.

Mitigation Strategy 1: Transitioning to CHIPS

For scenarios where you control both the primary TWA domain and the third-party api or assets domain, the recommended solution is to implement Cookies Having Independent Partitioned State (CHIPS). CHIPS allows you to opt-in a cookie to partitioned storage, meaning the cookie is isolated to the top-level site context where it was set.

When using partitioned cookies, a cross-site cookie set while a user is inside your TWA domain will be stored in a separate jar specific to your TWA domain. It cannot be read when the user visits other unrelated websites, satisfying privacy concerns while keeping your application functional.

To implement CHIPS, you must modify your server-side Set-Cookie headers to include the Partitioned attribute and the Secure attribute. For example:

Set-Cookie: session_id=abc123xyz; Secure; HttpOnly; SameSite=None; Partitioned;

Without the Partitioned and Secure markers, modern Chrome instances will reject the header entirely when executed inside a third-party context.

Mitigation Strategy 2: Utilizing the Storage Access API

If your TWA displays embedded third-party iframes that genuinely need access to their own first-party cookies (for example, a third-party chat widget or a billing platform), you must use the Storage Access API. This API allows embedded frames to request explicit storage access permissions from the user.

The iframe can programmatically check for and request access using JavaScript. The standard implementation pattern follows this layout:

document.hasStorageAccess().then(hasAccess => { if (!hasAccess) { return document.requestStorageAccess(); } }).then(() => { console.log("Storage access granted. First-party cookies can now be read."); }).catch(error => { console.error("Storage access denied:", error); });

On Android, depending on the Chrome version, this request may trigger a prompt inside the TWA window. Designing your UI to explain why this access is required ensures users do not prematurely deny the permission, which would break the integrated features.

Comparing Cookie Alternatives

When updating your application architecture, select the transition path that aligns with your domain structure. The following table highlights the primary options:

Moving Away from Web-Based Cookies for Native Operations

For long-term reliability of your TWA, the most robust architectural pattern is to phase out cookie-based session tracking for third-party endpoints altogether. Replacing cookie sessions with modern API tokens (such as JSON Web Tokens stored in LocalStorage or IndexedDB) eliminates the dependency on browser cookie policies entirely.

Because IndexedDB and LocalStorage are scoped strictly to your verified TWA domain, they are unaffected by third-party cookie blocklists. This approach ensures your authentication flows remain stable regardless of future browser privacy initiatives or changes to Chrome underlying engine policies.