Investigate and implement support for 'Related Origin Requests'

[Stormheg]

One of the main issues with Passkeys has been that they are scoped and only work with the Relying Part ID (domain) they are registered on. For example: if a user registers a Passkey on amazon.com, they won't be able to use it on amazon.de because the top level domain is different.

This appears to now be resolved in the form of 'related origin requests', see https://passkeys.dev/docs/advanced/related-origins/

Intended outcome

Investigate how to incorporate this feature.

Why is this important

I consider this feature a 'must have', most of the clients I would use this package with run the same site from multiple domains. They should be able to login using the same Passkey on all these domains.