A JWKS is defined at /.well-known/jwks.json

It's a JSON array of public keys which you can use to validate a JWT which is what an OIDC token is.

Making it an array means you can rotate keys whenever but the validator is typically caching the public keys.

https://www.hanko.io/blog/understanding-jwks

Actually... found it https://datatracker.ietf.org/doc/html/rfc6749

And here's a PHP implementation that is perfect. https://github.com/thephpleague/oauth2-client