User ID solutions: Where are we now?

Posted on Wednesday 07 September 2022 | IAB UK

As the end of third-party cookies draws closer, where are we when it comes to developing privacy-preserving alternative addressability solutions and what actions are available for you to take today?

IAB Tech Lab’s Project Rearc and Google’s Privacy Sandbox are the two main industry initiatives that are working to develop global solutions that work for all stakeholders, especially consumers. Read on for an update on each:

Project Rearc

Established by IAB Tech Lab in 2020, Project Rearc is a global effort that aims to ‘Rearchitect’ the digital advertising industry. As part of this, the group are coming together to build new accountability and addressability standards for our industry, with consumer privacy at the centre.


Building and maintaining trust in our industry plays a crucial role in us being able to sustain user level addressability. To achieve this, we need to be able to consistently demonstrate accountability and adherence to users’ data rights and privacy. IAB Tech Lab’s Rearc Accountability Working Group is working to establish technical mechanisms that fuel compliance programmes. There are four areas of work coming together to support an industry-wide accountability framework:

  1. A Global Privacy Framework: Leveraging IAB Europe’s Transparency and Consent Framework, this framework will standardise the recording and propagation of consumer privacy choices across markets, easing and improving compliance for all industry participants, even as regulation evolves.

  2. Accountability Programme Guidelines: These will be the standards of conduct that companies within the framework will need to adhere to for access to identifiers and personal data in the future.

  3. Technical Mechanisms + Auditable Data Structures: Traceable, tamper-proof signals and data structure that can be audited to ensure user privacy preferences have been respected throughout the supply chain.

  4. Attestation Framework: Systems and methods of ongoing automated testing to surface for industry participants erroneous or malicious non-compliance.


Alongside improving industry accountability, navigating the future of addressability is a fundamental part of Project Rearc’s work. The end of third-party cookies will lead to an ecosystem of both authenticated ‘logged in’ users with consumer-consented data, and anonymous users with very limited or no data.

Addressable, authenticated users

There are many parts of the internet today where users willingly log in or provide identifiable data on themselves to access content and services; and there are a number of publishers today who are moving to a signed-in model. Project Rearc are working on developing standards that will enable responsible use of these user-provided identifiers across a trusted supply chain. There are a number of commercial approaches available to the market, all of which are keen on setting a high bar for user privacy with accountability. Additionally, The Trade Desk have proposed a neutral, open-source, industry approach with its Unified ID 2.0 proposal. Commercial or otherwise, authenticated user standards will allow third parties to execute on behalf of trusted first parties, without enabling unauthorised third-party tracking and data collection.

Non-addressable, anonymous users

Contextual targeting has always played a key role in the marketing mix and with an increasing proportion of non-addressable audiences, this space is really growing. Project Rearc are working to develop standardisation around how we categorise content and communicate contextual signals in the bid process for scale in buying/selling when there is no ID available to third-parties. are closely involved in these conversations and the IAB Content Taxonomy plays a key role in these discussions.

First-party data audience attributes

Project Rearc are working on standards that will enable publishers who have first-party data on their audiences to make audience attributed data available in the bidding process when there is no ID available to third-parties. This will help publishers scale their data and add value to their audiences. Tech Lab are working with on these initiatives. are closely involved in these conversations and the IAB Audience Taxonomy and Data Transparency Standards play a key role in these discussions.

Find out more about how advertisers can harness the power of contextual targeting with IAB UK’s guide here. You can also find a webinar about the value of non-addressable audiences here.


Google’s Privacy Sandbox

Unlike Project Rearc, Privacy Sandbox focuses specifically on developing standards for the future non-addressable, anonymous web. The Privacy Sandbox team are working with the wider industry to find alternative methods to continue with key business functions, that currently rely on the third-party cookie, in a more privacy compliant way.

There are a number of initiatives within Privacy Sandbox as each business use case will require its own set of standards and processes to be able to continue, and companies will only be expected to adopt the initiatives that apply to them.

Privacy Sandbox: Actions to take today

The Conversion Measurement API for click-based measurement and the Trust Token API for user authentication and fraud detection are both available for the industry to get testing today. You can find out more information on how to do so via Google’s blog here.

Additionally, the Google ads team have published a whitepaper describing how its ads tools are testing clustering algorithms for generating cohorts for audience targeting using the principles defined by Chrome in the Federated Learning of Cohorts (FLoC) proposal. This proposal invites comments from the industry. The documentation can be found here.

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