Security advisory: Possible leak of legacy API keys via improper cache configuration

A CDN caching bug on RubyGems.org could hand one account’s API key to another person for up to an hour. If you signed in to RubyGems.org with a gem client older than v3.2.0, your key could have been exposed (the technical details are below). Currently, 18% of sign-ins through gem signin come from an affected version, and for the first several years of this bug, before we changed the client’s sign-in path in December 2020, it was every gem client.