This feature allows web developers to create WebAuthn[0] credentials (that is, "publickey" credentials, aka passkeys) in cross-origin iframes. Two conditions are required for this new ability: 1. The iframe has a publickey-credentials-create-feature permission policy. 2. The iframe has transient user activation. This will allow developers to create passkeys in embedded scenarios, such as after an identity step-up flow where the Relying Party is providing a federated identity experience. [0]: https://w3c.github.io/webauthn/
Enable web developers to build flows where WebAuthn credentials are created from within a cross-origin iframe (for example, for authenticated embeds, payment scenarios, etc). Currently web developers instead would have to fully redirect the user or open a pop-up window, neither of which are great experiences for embedded authn.