On Wed, May 8, 2024 at 3:50 PM Neil Madden <neil.e.mad...@gmail.com> wrote:
> On 8 May 2024, at 22:01, Joseph Heenan <jos...@authlete.com> wrote: > > > On 8 May 2024, at 21:43, Sam Goto <g...@google.com> wrote: > > > > On Wed, May 8, 2024 at 1:34 PM Joseph Heenan <jos...@authlete.com> wrote: > >> Hi Neil >> >> >> On 8 May 2024, at 18:45, Neil Madden <neil.e.mad...@gmail.com> wrote: >> >> >> On 8 May 2024, at 17:52, Sam Goto <g...@google.com> wrote: >> >> On Wed, May 8, 2024 at 7:23 AM Neil Madden <neil.e.mad...@gmail.com> >> wrote: >> >> >> >> >>> In particular, the call to the accounts endpoint assumes that the IdP is >>> willing to provide PII about the user to the browser. That seems >>> questionable. >>> >> >> Aside from a privacy/security threat model perspective (meaning, the user >> agent already has visibility over every network request made available to >> the content area) >> >> >> Sure, but if I use the recommended auth code flow or encrypted ID tokens, >> then PII is not exposed to the browser. And it’s not just the browser >> itself in the current proposal, as the token is exposed to javascript, of >> course, so the usual XSS risks. >> >> >> Sam’s response here is fair, but also note that as far as I understand it >> you can still use the authorization code flow or encrypted id tokens with >> the FedCM API >> > > That's correct: the browser doesn't open the response from the IdP to the > RP, so it can, for example, be encrypted. > > I was assuming that Neil was referring to the fact that the > id_assertion_endpoint (which contains the user's IdP's PII accounts > <https://fedidcg.github.io/FedCM/#dictdef-identityprovideraccount>) > become, suddenly, transparent to the browser. > > > Oh yes, that’s true - but (I think) the data from the > id_assertion_endpoint at least isn’t exposed to javascript and isn’t > vulnerable to XSS? > > > That depends on whether the IdP correctly enforces the presence of the > sec-fetch-dest header. If it doesn’t then yes, it would be vulnerable. > Presumably it’s also vulnerable on older/niche browsers that don’t block > sec-* headers: caniuse.com reckons > 8% of users globally are using > browsers that don’t understand any sec-fetch-* headers. I’m not sure when > sec-* was added to the forbidden list. > > I guess, flipping this around, we might ask what is the legitimate purpose > for which browsers need to access the user’s name, email address (both > requires) and other identifying information? I’d have thought an identifier > (possibly randomised) and some user-supplied account nickname would be > sufficient. > That's easier to answer: the browser needs name/email/picture to construct an account chooser <https://docs.google.com/presentation/d/1iURrPakaHgBfQ6mAefKijjxToiTTgBSPz1rtaV0od98/edit#slide=id.p>, which is the UX that tested best with users by a far margin. Static/unpersonalized permission prompts - example <https://www.cookiestatus.com/images/content/storage-access-api.jpg> in Safari, example <https://developers.google.com/static/privacy-sandbox/assets/images/storage-access-api-permission-prompt.png> in Chrome - perform extremely poorly (in comparison to account choosers), although have other benefits too (namely ergonomics and extensibility), so Chrome (and others) expose that too in the form of the Storage Access API <https://developer.mozilla.org/en-US/docs/Web/API/Storage_Access_API>. > > — Neil > >
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