I figured out how to manually get the SSO token. Navigate to https://<your org>.zoom.us/saml/login?from=desktop. Then login. The resulting page will contain a link with id “sso-button” and href"zoommtg://<your org>.zoom.us/sso?token=<The SSO token>"
It would be nice if there were some automated way to get SSO tokens, and I would have appreciated it if there were some documentation about this. It took me a while to figure out. But this seems to work (at least for now).