Based on MSA-20-0005 note, I went ahead in my moodle dev box and manually update the MathJax URL in site administration -> plugins -> filters -> mathjax settings using the patched version https://firstname.lastname@example.org/MathJax.js, but failed. The system basically is in js code mode, not usable.
My moodle dev is running Moodle 3.6.3. The default/original "filter_mathjaxloader | httpsurl" was "https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.2/MathJax.js"
I don't know how to move forward or revert the httpsurl value to get out of there.