Permissions-Policy header for Google “Topics API”

[dmarti]

This is an update of #266.

The new Permissions-Policy header to opt out of the "Topics API" tracking system that replaces Google FLoC, is:

Permissions-Policy: browsing-topics=()

More info: https://github.com/patcg-individual-drafts/topics

"Topics API" is scheduled to be made available to all Google Chrome users in mid-2023, which means that sites developed now are likely to be deployed to production when "Topics API" is already active.

According to Peter Snyder, Sr. Director of Privacy for the Brave web browser, Topics API is "Rebranding FLoC Without Addressing Key Privacy Issues".

Most sites will not need to participate in cross-site tracking of users by interests, and people who do want their site to participate in "Topics API" can easily remove the header.

[dmarti]

Some people have expressed concerns that opting out of "Topics API" will affect their site's ranking in Google Search. Google recently confirmed to the Competition and Markets Authority in the UK that "Google Search will not use a site's decision to opt-out from the Topics API as a ranking signal." (see p. 34 of Privacy Sandbox Progress Report for October - December 2022).