Optional[customOptional[unknownLiterally json, which represents JWKS with public keys for JWT verification. It worth mentioned that in a case of adding/rotating keys the jwk_set_json also should be updated here. Besides, the "issuer" parameter should be set even if the JWKS will be resolved locally.
It's not required provider OIDC issuer should be real OIDC provider, but should expose OIDC configuration with "/.well-known/openid-configuration" endpoint. Configuration should contains the "jwks_uri" endpoint where the JSON Web Key Set (JWKS) can be found; this set contains public keys used to verify JSON Web Tokens (JWTs) issued by an identity provider.
Limitations for external OIDC providers: