Excellent! Thanks for sharing. A +1 to ya, Noah!
CentOS/RHEL have since fixed by re-issuing nss-sfotoken files (there are two) in updates ... of course, if yum is broken, makes it hard to fix it. Thus, the 'fix' to 'fix' yum is in the link provided by Noah. And a comment ... first time in 15 years that I've experienced such a thing. Rare hickup.
'spirit of sharing', Ken