Intent to Ship: FedCM (was WebID)

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Sam Goto

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3 באוק׳ 2022, 18:31:083.10.2022
עד blink-dev

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The Federated Credential Management API (originally WebID) allows users to use their federated identity to login to websites in a manner compatible with improvements to browser privacy. This intent covers a Web Platform API to prompt the user to choose accounts from one Identity Provider to sign-up or sign-in to a website. We expect to send future intents to make enhancements over these capabilities (e.g. multiple IdPs) and keep raising the privacy properties of the API (e.g. the timing attack problem).

Blink component


TAG review

Early Tag Review 

Spec Tag Review

TAG review status



Interoperability and Compatibility

   Zero compatibility risk (new API)

Gecko: Positive

WebKit: Positive

On interoperability and forward compatibility: FedCM is large and complex and, as browser vendors start to implement it (example), we are seeing positive and constructive engagement. For example, we are actively working with Mozilla to find an interoperable way to address the timing attack problem, support multiple IdPs and protect endpoints. Because of that, there is a risk of incompatible changes going forward (list of currently known potential risks here), mostly affecting IdPs (see section below on activation). We think it is unavoidable that parts of our current design are suboptimal and are going to need to be revisited, but the biggest risk we are trying to avoid is to fail to bring IdPs along with us, increase their production footprint that we can learn from, and increase our confidence on technical feasibility and product-market fit.

Based on our origin trials, we expect a small number of IdPs (say, less than ~30) to be incentivized  to use the API in production until chrome phases-out third party cookies in 2024. These IdPs that we are partnering with need time, confidence, and stability to increase their deployment. For example, in origin trials, we ran into CSP issues and cross-origin iframe issues that we could have never anticipated without IdPs experimentation, even if we had interoperable implementations in all major browsers. We think that the risk we take by not having a baseline that IdPs can work from if the API isn’t shipped outweighs the forward compatibility risks: not shipping would mean that we won’t learn about these bugs until it is too close to the deprecation of third party cookie (e.g. IdPs will continue to evolve their products using iframes and third party cookies without an alternative to build on). We also think that we can address some concerns on forward compatibility by setting the right expectations during developer documentation / outreach to IdPs as we make it battle-tested before we deprecate third party cookies in 2024.

Web developers: We’ve been working with Identity Providers and Relying Parties over the last ~3 years, going over a good amount of design alternatives and prototypes (TPAC 2020, 2021 and 2022, BlinkOn 14, 15, 16, OIDF 2020, IIW 2020), trying to strike the right balance between privacy/security properties and deployment structures (e.g. backwards compatibility). The current formulation is the result of identity providers, relying parties, browser vendors and industry experts that have co-designed with us through our devtrials and gathered production experience with their users through our origin trials (around ~33 small and big registered IdPs). For example, in the last two quarters, the Google Sign-in team has run experiments with ~20 Relying Parties leading to more than ~300K real users logging-in in production, achieving comparable sign-in/up conversion rates without depending on third party cookies. While this is a small sample size of the ecosystem and the deployment (notably missing representation of enterprises and EDU), we are encouraged by the approach and confident this is a solid and necessary first step.

Other signals: This API is being developed within the FedID CG composed of identity providers, relying parties, browser vendors and industry experts. The CG has produced an enumeration of known issues in the absence of third party cookies, a list of mitigation alternatives and is actively working on how to decide which Web Platform API to use for each circumstance. We don’t expect (or are designing for) FedCM to be used exclusively to solve all of the known issues, but rather in coordination with other browser proposals (e.g. CHIPS). We acknowledge that there is a series of anticipated breakages that are not handled (effectively) by any proposal (FedCM included) at the moment, and we are excited to continue working with the FedID CG, the Privacy CG and the Privacy Sandbox to extend FedCM in whichever way is constructive and/or work on new proposals.


Our design assumes that it is exponentially harder, in this order, to make changes to (a) user behavior than, (b) websites, (c) identity providers and then, lastly, (d) browsers. 

So, the design pulls as much as possible the burden of change to browsers vendors and identity providers, and goes to a great extent to require little to no changes to websites and user's norms, while at the same time, raising the privacy properties of the system.

While that’s not always possible, we believe we found an activation structure that could work at scale for a substantial part of the deployment (especially for consumers) through JS SDKs that are provided by Identity Providers and get dynamically embedded into relying parties.

For example, through their JS SDKs, the Google Sign-in team was able to replace their dependence on third party cookies with FedCM without requiring changes to relying parties.

We acknowledge that this activation model is insufficient for a lot of the deployment (especially for enterprises), so finding alternative activation structures is an active area of investigation.

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

This API does not deprecate or change behavior of existing APIs.


Basic devtools integration supported. We plan to extend this support as the product matures and we learn from developers what challenges they run into.

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?


The current implementation is available on all platforms (Windows, Mac, Linux, ChromeOS and Android) except WebView.

Is this feature fully tested by web-platform-tests?

Yes, fedcm-* tests in this directory.

Known issue: some of our WPT tests are failing on While the tests exist and pass in Chromium’s infrastructure, they rely on a Chrome-specific flag that would not work in other browsers. Making them work on upstream WPT requires PAC support; however, WPT’s PAC support does not currently support HTTPS tests, which FedCM requires because it is only exposed to secure contexts. We are working on adding that support, which is in progress here.

Origin Trial Instructions

Flag name


Requires code in //chrome?


Tracking bug

Launch bug



Estimated milestones

OriginTrial desktop last


OriginTrial desktop first


OriginTrial Android last


OriginTrial Android first


DevTrial on Android


Anticipated spec changes

We’re also currently resolving some questions related to Fetch integration.

Link to entry on the Chrome Platform Status

Links to previous Intent discussions

This intent message was generated by Chrome Platform Status.

Rick Byers

לא נקראה,
3 באוק׳ 2022, 22:13:303.10.2022
עד Sam Goto,blink-dev
I've been involved somewhat with this work and so I'm recusing myself from my API owner role for this intent.

Nevertheless I wanted to chime in and say that I agree with the risk tradeoff the team is proposing we make here. Yes there's still a lot to figure out in the federated identity space, and it's likely that we'll find places where we need to make some breaking changes to better meet customer needs and get to interoperability. But I believe shipping what we have now as a V0 is the most effective way to figure out the path forward in a timeframe that's compatible with Chrome's plans for 3P cookie deprecation. We've been evolving designs in public for >2 years and now we have at least one partner who is ready to scale up beyond OT limits, and we'd both learn a lot from doing so. It would be a mistake to think that we just have a few open issues to resolve before we could call the design "mature", and I don't want to risk losing momentum with customers by suggesting we should just stick to "experiments" for another 6-12 months. Instead the process of becoming mature in the context of a dynamic identity provider ecosystem and evolving privacy landscape will be best served by a "launch and iterate" approach. Doing this responsibly requires a commitment on our part to engage with the standards community in good faith to avoid past failure modes where V0 (chromium-only) and V1 (standard) APIs have co-existed in chromium for an extended period of time while Google services in particular have retained a dependency on the V0 behavior.

The partnership and ecosystem dynamics here remind me a lot of what we encountered with PaymentRequest. We still don't have payment APIs "figured out", but we've been able to learn and iterate by working with a handful of partners through the web payments working group to evolve fully launched APIs, including making significant breaking changes along the way (despite my own initial skepticism of the practicality of that).


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Yoav Weiss

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5 באוק׳ 2022, 4:25:385.10.2022
עד Rick Byers,Sam Goto,blink-dev
I agree with this ordering.
It'd be good to be transparent with adopting identity providers about the potential compat risk, so that they'd know what they are signing up for.

On top of that, there's some risk of the compat issues leaking from identity providers to websites, if those websites self-host the IDP SDKs (for performance or other reasons).
Would it be possible to ask identity providers to take measures against self-hosting? e.g. I think `document.currentScript.src` can help them enforce the script coming from an updatable source.

Sam Goto

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5 באוק׳ 2022, 16:54:095.10.2022
עד Yoav Weiss,Rick Byers,blink-dev

I really like the `document.currentScript.src` suggestion, and I think that’s a great way to help us control future breakages!

As you suggested, there is a lot that we can do by working with the Developer Relations (devrel) and Business Development (BD) teams to set up the right expectations as this goes out. Here are a few examples that we think could work:

  • Set up a communication channel (e.g. a mailing list similar to the one we have for Core Web Vitals here and here) that IdPs can subscribe to coordinate with us (in addition to direct 1:1 partnerships)

  • Be transparent about the moving parts (e.g. the timing attack problem, the multi-IdPs API, etc), and a rough timeline to resolve them (e.g. we could use the Privacy Sandbox Timeline and have meaningful stability checkpoints at General Availability in 2023 and Phase-out in 2024).

  • Make a recommendation to IdPs to control their SDKs (e.g. either through document.currentScript.src or SLAs), at least until some moving parts settle, so that we can iterate quickly as an industry. It is ultimately a business decision that IdPs make, so we can only go as far as making a recommendation.

Just a few more data points:

  • We expect it is going to take us more than a quarter but less than a year to resolve the known moving parts with confidence. Also, importantly, they may or may not require backwards incompatible API changes.

  • To give you a sense of numbers, in origin trials, ~33 IdPs registered over the last ~7 months. There are few IdPs (that have the incentives to use the API at the moment, while 3P cookies are still around) and they are large and sophisticated developers

  • In our experience so far, very few websites choose to self-host (in origin trials, we found only 1), and the ones that do, are extremely large and sophisticated developers that can afford to self-host (i.e. we would know how to reach out to them individually)

  • Outside of real-world production IdP deployment, it is possible, though, that we are going to find developers playing with the API, writing blogs or demos, and that’s more likely to break (because we wouldn’t be able to reach out to them individually), but that’s a more acceptable breakage.

Ilya Grigorik

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11 באוק׳ 2022, 19:20:3211.10.2022
עד Sam Goto,Yoav Weiss,Rick Byers,blink-dev
At Shopify, we've followed progress closely, and I'm really excited to see the i2s! 

Agree with the analysis tradeoffs and proposed rollout. This is a capability we're keenly interested in and would be willing to stay hands-on with as it evolves.

Daniel Bratell

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12 באוק׳ 2022, 12:02:2112.10.2022
עד Ilya Grigorik,Sam Goto,Yoav Weiss,Rick Byers,blink-dev


(I appreciate that there are some unique risks here, but I'm confident the team will be able to navigate those)


Chris Harrelson

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12 באוק׳ 2022, 12:16:1612.10.2022
עד Daniel Bratell,Ilya Grigorik,Sam Goto,Yoav Weiss,Rick Byers,blink-dev

Yoav Weiss

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12 באוק׳ 2022, 12:43:0512.10.2022
עד Chris Harrelson,Daniel Bratell,Ilya Grigorik,Sam Goto,Rick Byers,blink-dev

The risk/benefit tradeoff here seems reasonable. Thanks for continuing to work with the community on finding the ideal shape of the solution here.
Please recommend IDPs to take anti-self-hosting means to prevent making future changes to this harder than they should be.

Sam Goto

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13 באוק׳ 2022, 14:18:0513.10.2022
עד Yoav Weiss,Chris Harrelson,Daniel Bratell,Ilya Grigorik,Rick Byers,blink-dev
Thanks you all for the thoughtful and timely review, and we'll follow up on the action items here separately!


Erik Anderson

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19 בינו׳ 2024, 18:11:0419 בינו׳
עד blink-dev,Sam Goto,Chris Harrelson,Daniel Bratell,,,blink-dev,
Hi everyone,

The Microsoft Edge team was recently queried by an IDP about Microsoft Edge's support status for FedCM. We are also shipping it and will continue to support it.

If you're an RP or IDP building support for Chrome, you should assume that your scenario will work equally well in Microsoft Edge. If you run into issues specific to Microsoft Edge, we will investigate and resolve them.

p.s. Sorry for reviving an otherwise long-dormant thread; with so many other intents for additions to the API this one made the most sense to provide a general statement about our shipping status.
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