@Gil Thanks for reaching out and sincere apologies for the delay on this. We are constantly trying to reduce our answer time and in coming days you will see a significant improvement here. So we appreciate you posting your future queries here.
Currently cache-control is bye default private and it cannot be changed.
We welcome you to submit this as feedback on our Azure AD B2C feedback page for further consideration. Once done, do update the feedback URL here, so that other people can also vote for it.
https://feedback.azure.com/forums/169401-azure-active-directory/category/160596-b2c
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