Update ROR docs for brownfield to address both ROR not supported, and different RP IDs

[timcappalli]

Issue with existing content

Link to content

https://passkeys.dev/docs/advanced/related-origins/

What is the issue?

The current ROR brownfield docs collapse different RP IDs and client not supporting ROR into the same solution set (redirecting the user). In cases where the browser does support ROR, but the RP ID for the user's passkey is different, there is no need to redirect the user. You can make a WebAuthn request with the RP ID of the passkey, assuming the calling page's origin is in the well-known for that new RP ID.

Proposed changes

Document the client support ROR path without a redirect.

Any other notes