The logic for the cache in `JwtRealm` produces a broken `Cache` instance to some degree. 
We create a `BytesArray` from the user credential hash:

```java
            final BytesArray jwtCacheKey = isCacheEnabled() ? new BytesArray(jwtAuthenticationToken.getUserCredentialsHash()) : null;
            if (jwtCacheKey != null) {
                final User cachedUser = tryAuthenticateWithCache(tokenPrincipal, jwtCacheKey);
```

and use it as as a cache key in a `Cache` instance down the line.
But then we also clear the bytes in that `BytesArray` to `0` in org.elasticsearch.xpack.security.authc.jwt.JwtAuthenticationToken#clearCredentials. 

This leads to the hash map in the `Cache` getting filled with loads of `BytesArray` that all have the same 0-filled content but that were not equal to each other when first inserted into the map, causing the map to put them all in the same bucket.

<img width="1233" alt="image" src="https://github.com/elastic/elasticsearch/assets/6490959/86a914d7-a2d4-4b01-ad99-e0d14e71a58b">

ref path to the broken map:

<img width="1436" alt="image" src="https://github.com/elastic/elasticsearch/assets/6490959/87ac6f78-bc09-41c4-9a79-28fbbd14f6e6">

x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/authc/jwt/JwtRealmTestCase.java
+ JwtRealmInspector.getClientAuthenticationType(jwtRealm)
                + "], clientSecret=["
                + JwtRealmInspector.getClientAuthenticationSharedSecret(jwtRealm)
                + "], iss=["
                + JwtRealmInspector.getAllowedIssuer(jwtRealm)
                + "], aud="
                + JwtRealmInspector.getAllowedAudiences(jwtRealm)
                + ", algsHmac="
                + JwtRealmInspector.getAllowedJwksAlgsHmac(jwtRealm)
                + ", filteredHmac="
                + JwtRealmInspector.getJwksAlgsHmac(jwtRealm).algs()
                + ", algsPkc="
                + JwtRealmInspector.getAllowedJwksAlgsPkc(jwtRealm)
                + ", filteredPkc="
                + JwtRealmInspector.getJwksAlgsPkc(jwtRealm).algs()
                + ", claimPrincipal=["
                + JwtRealmInspector.getPrincipalClaimName(jwtRealm)
                + "], claimGroups=["
                + JwtRealmInspector.getGroupsClaimName(jwtRealm)
                + "], authz=["
                + jwtRealm.delegatedAuthorizationSupport.hasDelegation()
                + "], meta=["
                + JwtRealmInspector.shouldPopulateUserMetadata(jwtRealm)
                + "], jwkSetPath=["
                + JwtRealmInspector.getJwkSetPath(jwtRealm)
                + "]."
        );
        for (final JWK jwk : JwtRealmInspector.getJwksAlgsHmac(jwtRealm).jwks()) {
            logger.info("REALM HMAC: jwk=[{}]", jwk);
        }