Backport #31874 by @bohde
In the OpenID flows, the "CfTurnstileSitekey" wasn't populated, which
caused those flows to fail if using Turnstile as the Captcha
implementation.
This adds the missing context variables, allowing Turnstile to be used
in the OpenID flows.
Co-authored-by: Rowan Bohde <rowan.bohde@gmail.com>