PKCE + Passwordless with Embedded/Custom Template Universal Login - help needed

Hey, I have a particular case - we’d like to setup Passwordless flow for a SPA but need a custom behaviour (switch between sms/email) on the login page - I found the following options:

In both cases I would use auth0.js - after passwordlessLogin as I understand, I should receive authorizationCode to exchange for token using oauth/token afterwards.

But it seems that auth0.js has no support PKCE support which we also need.

Is it possible to do?
If so, can you point me to relevant documentation or provide a simple explanation of the flow?

Many thanks.