io.micronaut.security:micronaut-security-oauth2 has invalid IdTokenClaimsValidator logic on aud

Summary

IdTokenClaimsValidator skips aud claim validation if token is issued by same identity issuer/provider.

Details

See https://github.com/micronaut-projects/micronaut-security/blob/master/security-oauth2/src/main/java/io/micronaut/security/oauth2/client/IdTokenClaimsValidator.java#L202

This logic violates point 3 of https://openid.net/specs/openid-connect-core-1_0.html#IDTokenValidation.

Workaround exists by setting micronaut.security.token.jwt.claims-validators.audience with valid values.
micronaut.security.token.jwt.claims-validators.openid-idtoken can be kept as default on.

PoC

Should probably be:

                return issuer.equalsIgnoreCase(iss) &&
                        audiences.contains(clientId) &&
                                validateAzp(claims, clientId, audiences);

Impact

Any OIDC setup using Micronaut where multiple OIDC applications exists for the same issuer but token auth are not meant to be shared.

Mitigation

Please upgrade to a patched micronaut-security-oauth2 release as soon as possible.

If you cannot upgrade, for example, if you are still using Micronaut Framework 2, you can patch your application by creating a replacement of IdTokenClaimsValidatorReplacement

package cve;

import io.micronaut.context.annotation.Replaces;
import io.micronaut.context.annotation.Requires;
import io.micronaut.core.annotation.NonNull;
import io.micronaut.core.util.StringUtils;
import io.micronaut.sec…