Contact emails

n...@chromium.org

Explainer

https://github.com/fedidcg/FedCM/issues/428 

Specification

https://github.com/fedidcg/FedCM/pull/547 

Summary

The fetches in the FedCM API are hard to reason about because of the 
properties required of them. While there is ongoing discussion regarding 
the accounts endpoint, there is broad consensus that the ID assertion 
endpoint should use CORS. This aligns security properties of this fetch 
more closely to other fetches in the web platform.

Blink component

Blink>Identity>FedCM 
<https://g-issues.chromium.org/issues?q=status:open%20componentid:1456331&pli=1&authuser=0>

TAG review

Not requesting a TAG review. We have already had extensive discussions with 
Fetch experts.

TAG review status

N/A

Risks

Interoperability and Compatibility

This is a backwards incompatible feature, but one that is warranted due to 
consensus reached by our security reviewers as well as other browser vendor 
engineers. We have a manageable list of IDPs that we know are using the 
FedCM API and we have reached out to all IDPs that are currently deploying 
FedCM to make sure that they won’t break with this change.


Gecko: Positive based on TPAC discussions and 
https://github.com/fedidcg/FedCM/issues/428. Not filing a standards 
position request for small additions at the explicit request from Firefox 
(they prefer PRs).

WebKit: Positive based on TPAC discussions and 
https://github.com/fedidcg/FedCM/issues/428. Recently, standards position 
requests for smaller FedCM features have been closed, pointing to the 
(unresolved) main FedCM one in 
https://github.com/WebKit/standards-positions/issues/309 so not filing one 
for this.

Web developers: No signals

Other signals:

Ergonomics

N/A


Activation

N/A


Security

By adding CORS, we add a check that the IDP explicitly agrees for the 
browser to share the ID assertion response to the RP. In addition, having 
this fetch align with most other credentialed fetches in the browser means 
that any future protections are received by default, and we do not have to 
special case this fetch.


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?

None


Debuggability

We surface errors when there is a network problem with the ID assertion 
fetch. This will help developers understand when this feature introduces a 
problem in their FedCM calls.


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

No. FedCM is not supported on Android WebView.

Is this feature fully tested by web-platform-tests 
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>
?

https://wpt.fyi/results/credential-management/fedcm-identity-assertion-nocors.https.html?label=experimental&label=master&aligned
 
(will pass on Chrome once we ship)

Flag name on chrome://flags

None

Finch feature name

FedCmIdAssertionCORS

Requires code in //chrome?

True (because FedCM API does)

Tracking bug

https://issues.chromium.org/issues/40284123

Estimated milestones

DevTrial on desktop

120


DevTrial on Android

120

We want to ship on M124

Anticipated spec changes

Open questions about a feature may be a source of future web compat or 
interop issues. Please list open issues (e.g. links to known github issues 
in the project for the feature specification) whose resolution may 
introduce web compat/interop risk (e.g., changing to naming or structure of 
the API in a non-backward-compatible way).

https://github.com/whatwg/fetch/issues/1637

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5094763339710464

This intent message was generated by Chrome Platform Status 
<https://chromestatus.com/>.

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