Explainer

https://github.com/w3c-fedid/FedCM/blob/main/explorations/drafts/interception.md

The explainer

• Includes the information requested by the Explainer Explainer.
• Follows the Web Platform Design Principles.
• Includes or links to answers to the Security/Privacy Questionnaire.
• Describes user research you did to validate the problem and/or design.

Where and by whom is the work is being done?

• GitHub repo: https://github.com/w3c-fedid/FedCM/blob/main/explorations/drafts/interception.md
• Primary contacts:
  • Sam Goto (@samuelgoto), Google, Author
• Organization/project driving the design: Google Chrome
• This work is being funded by: Google
• Incubation and standards groups that have discussed the design:
  • FedID CG
• Standards group(s) that you expect to discuss and/or adopt this work when it's ready: FedID WG

Feedback so far

• Multi-stakeholder feedback:
  • Chromium comments: https://groups.google.com/a/chromium.org/g/blink-dev/c/_5P00uaafKM
  • Mozilla comments: not yet
  • WebKit comments: not yet
• Major unresolved issues with or opposition to this design:
  • We ran a session at TPAC in Kobe (notes)

You should also know that...

This proposal intends to help enable IdPs to deploy FedCM on all of its RPs without requiring the RPs to redeploy.

There are a few reasons why we think deploying FedCM at scale might be important:

• First, we think this can remove one of the main blockers to combat bounce tracking, which relies on top-level link-decorated navigations in conjunction with first party cookies. With this proposal deployed at scale, browsers get closer to be able to remove one of those two components, at least for a meaningful part of the traffic that is required to preserve federation.
• Second, we are finding that the built-in native FedCM UX often outperforms top-level navigations (specially on mobile), so we'd expect that this will be useful present a better user experience to IdPs/RPs and users, in and of itself.
• Third, in agentic browsers, whenever FedCM is being used, we think we can turn federation into a structured/programmable tool (like an MCP), rather than unstructured computer-use actuation (like computer vision), fundamentally providing a better foundation to agentic browsers when it comes assisting users logging in to websites.

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