Intent to Experiment: FedCM Auto Re-Authentication API

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Yi Gu

Feb 15, 2023, 9:28:14 PM2/15/23
to blink-dev

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An extension to the existing FedCM API that allows a website to provide its preference for a streamlined UX (automatically, rather than explicitly, re-authenticating the user) when their users return to them. The API design requires that the preference is only respected for returning users, that is if the user has previously and explicitly granted permission for the Relying Party (RP) and Identity Provider (IdP) communication in the browser through a FedCM call.

Blink component

Blink > Identity > FedCM

TAG review

TAG review status



Interoperability and Compatibility

Gecko: we have been actively working with Firefox to standardize this API. In general we are aligned on the feature itself. e.g. auto re-authentication can provide streamlined UX without reducing privacy. Meanwhile, there are some open questions about what API is more suitable to achieve this goal. e.g. Firefox proposed to reuse the “mediation mode” in Credential Management API which is a promising direction as well. We will keep evaluating all the proposals and reach an alignment before shipping.

WebKit: No signal for “auto re-authn” yet. Positive for the general FedCM API.

No compatibility risk from an API’s perspective. Auto re-authn is supported by adding a new boolean to the existing FedCM API which is default to false (defaults to the existing behavior).

On cross-browser interoperability, because the Auto re-authn API simply controls a UX preference suggested by the relying party, the UA may choose not to respect  it (for example, either across all relying parties or through browser settings) and fallback to the existing sign-in flow that requires an explicit user confirmation.

Overall, this is a small addition to the FedCM API, and as such mostly inherits the interop and compatibility risks from that API. See for the discussion.


Similar to the FedCM API, we deliberately leave the bulk of the work to the IdP to ensure that minimal RP change is needed (no RP change is needed for IdPs who have already supported similar flow). 

This feature, specifically, is one that can be currently controlled by JS SDKs, so we expect activation to have a similar profile as FedCM: immediately enabled to websites (without any redeployment) by IdPs making use of it (by redeploying their JS SDKs).

WebView Application Risks

N/A as this feature is not available on WebView.

Goals for experimentation

To learn whether the new streamlined re-authentication experience performs well with users. We are planning to collect the following data points:

  • number of successful re-authentication flows, 

  • how often a user may want to terminate the flow,

  • reasonable time for cooldown


Besides regular FedCM support, we show error messages stating why auto re-authn is unavailable. 

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


Similar to FedCM API, we expect the feature to be available on all platforms (Windows, Mac, Linux, ChromeOS and Android) except WebView.

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

Yes. (we’re still working on making tests behave as intended on

Flag name


Requires code in //chrome?


Tracking bug

You can track our progress here:

Launch bug

Estimated milestones


Link to entry on the Chrome Platform Status

Mike Taylor

Feb 16, 2023, 1:14:34 PM2/16/23
to blink-dev, Yi Gu
Hi Yi,

Is this a request for an Origin Trial, or are you requesting to ship for some percentage of Stable users? 

Yi Gu

Feb 16, 2023, 1:34:18 PM2/16/23
to Mike Taylor, blink-dev, Yi Gu
Hi Mike, this is for an Origin Trial.

Mike Taylor

Feb 21, 2023, 8:27:33 PM2/21/23
to Yi Gu, blink-dev

(Apology for the delay in responding...) I only see M112 listed as a milestone. If this is the beginning of the OT, how many milestones do you intend to support?


Yi Gu

Feb 21, 2023, 8:47:36 PM2/21/23
to Mike Taylor, Yi Gu, blink-dev
Hi Mike

Our plan is to run the origin trial from M112 to M114 (inclusive).


Mike Taylor

Feb 22, 2023, 10:44:11 AM2/22/23
to Yi Gu, blink-dev

LGTM to experiment from 112 to 114 inclusive.

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