IdP sign-up

[obfuscoder]

Let's say, an End-User wants to signup ad a Relying Party and the RP only connects to specific IdPs the End-User does not have an account on. Nowadays, the End-User can simply choose one of the IdPs and ad-hoc create an account there (register at IdP) in the flow.

With FedCM this seems to be impossible as the End-User must have been logged into the IdP previously for it in order to show up in the list of possible accounts/identities to choose from. Even if the RP is enlisting all IdPs it supports, the End-User would be required to open a separate browser tab and do a IdP sign-up there before it can continue on the current browser tab with the actual process.

[npm1]

This is a duplicate of #283 so I'll close this one.