I just confirmed with our engineering team that this is not something we support, and likely never would as passing a passphrase in plain text in a URL query string is very insecure.
With that said, you do bring up an interesting use-case and I will make sure that we take that into consideration for future iterations of sharing for review with Frame.io.
Have you considered the potential security risks of including a passphrase directly in the URL as a query parameter? Could this expose sensitive information if the URL is shared publicly?