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Consent
Cross-Device Identity

Cross-device identity reconciliation

When users interact with your product across multiple devices — web browsers, mobile apps, connected TVs, and tablets — each device typically generates its own anonymous fides_user_device_id. Without identity linking, this creates fragmented consent records: the same person may appear as four separate users with conflicting privacy preferences.

Fides solves this through cross-device identity reconciliation. When a user authenticates (e.g., logs in with an email address), Fides merges all associated device identities into a single unified profile. From that point on, any preference query — by device ID or email — returns the same consistent result.

This workflow uses the pre-verified consent endpoint (PATCH /api/v1/privacy-preferences/pre-verified), which accepts both a fides_user_device_id and a verified identity (such as email) in a single call. This is the recommended approach for server-side integrations where the user's identity has already been verified by your authentication system.

Walkthrough

Step through the scenario below to see how four anonymous device records are progressively linked into a single identity as the user authenticates on each platform.

Website
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Mobile App
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Connected TV
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Tablet App
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Unified Identity

The Problem: Fragmented Consent

Cookie House Network operates across web, mobile, connected TV, and tablet. Each platform collects privacy preferences independently using anonymous device IDs. The same user may have conflicting preferences scattered across four separate records.

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How it works

  1. Anonymous collection — Each platform saves consent via PATCH /api/v1/privacy-preferences using only the device's fides_user_device_id. At this stage, Fides treats each device as a separate user.

  2. Authenticated linking — When a user logs in, the platform calls PATCH /api/v1/privacy-preferences/pre-verified with both the fides_user_device_id and a verified identifier (e.g., email). Fides creates or extends a unified identity graph that links the device ID to the email.

  3. Preference merging — As additional devices authenticate with the same email, they are merged into the existing identity. The most recent preference associated with the unified identity becomes the canonical value.

  4. Consistent reads — GET /api/v1/current-privacy-preferences with any linked identifier (device ID or email) returns the same unified preference record.

  5. Cross-device propagation — When the user updates their preference on any linked device, the updated value is available to all other devices on their next read from Fides.

Related resources

Consent APIConsent API (v3)