Introduction

In order to prevent cross-site user tracking, browsers are partitioning all forms of storage (cookies, localStorage, caches, etc). But, there are many legitimate use cases currently relying on unpartitioned storage that will vanish without the help of new web APIs. We’ve seen a number of APIs proposed to fill in these gaps (e.g., Conversion Measurement API, Private Click Measurement, Storage Access, Trust Tokens, TURTLEDOVE, FLoC) and some remain (including cross-origin A/B experiments and user measurement). We propose a general-purpose, low-level API that can serve a number of these use cases.

The idea is to provide a storage API (named Shared Storage) that is intended to be unpartitioned. Origins can write to it from their own contexts on any page. To prevent cross-site tracking of users, data in Shared Storage may only be read in a restricted environment that has carefully constructed output gates. Over time, we hope to design and add additional gates.

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