>3. CLIENT uses it's identity to request token from ISSUER/ATTESTER
The ISSUER and ATTESTER are different roles. As previously quoted, "Clients explicitly trust Attesters to perform attestation correctly and in a way that does not violate their privacy." The RFC is explicit that, when all of the roles are held by the same entity, the attestation should not rely on unique identifiers. But that's exactly what a session cookie is.
>You can see how the ISSUER/ATTESTER can identify the client as the source of the "anonymous request" to the ORIGIN because the ISSUER, ATTESTER and ORIGIN are the same entity, and therefore it can use a timing attack to correlate the request to the ORIGIN (1.) with the request to the ISSUER/ATTESTER (3.).
No timing or spacing attack is needed here. If I have to provide Kagi with a valid session cookie in order to get the tokens, then they already have a unique identifier for me. There is no guarantee that Kagi is not keeping a 1-to-1 mapping of session cookies to ISSUER keypairs, or that Kagi could not, if compelled, establish distinct ISSUER keypairs for specific session cookies.
The ISSUER and ATTESTER are different roles. As previously quoted, "Clients explicitly trust Attesters to perform attestation correctly and in a way that does not violate their privacy." The RFC is explicit that, when all of the roles are held by the same entity, the attestation should not rely on unique identifiers. But that's exactly what a session cookie is.
>You can see how the ISSUER/ATTESTER can identify the client as the source of the "anonymous request" to the ORIGIN because the ISSUER, ATTESTER and ORIGIN are the same entity, and therefore it can use a timing attack to correlate the request to the ORIGIN (1.) with the request to the ISSUER/ATTESTER (3.).
No timing or spacing attack is needed here. If I have to provide Kagi with a valid session cookie in order to get the tokens, then they already have a unique identifier for me. There is no guarantee that Kagi is not keeping a 1-to-1 mapping of session cookies to ISSUER keypairs, or that Kagi could not, if compelled, establish distinct ISSUER keypairs for specific session cookies.