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
final User user = randomFrom(jwtIssuer.principals.values());
        logger.info("USER[" + user.principal() + "]: roles=[" + String.join(",", user.roles()) + "].");
        return user;
    }
    protected SecureString randomJwt(final JwtIssuerAndRealm jwtIssuerAndRealm, User user) throws Exception {
        final JwtIssuer.AlgJwkPair algJwkPair = randomFrom(jwtIssuerAndRealm.issuer.algAndJwksAll);
        final JWK jwk = algJwkPair.jwk();
        logger.info(
            "ALG["
                + algJwkPair.alg()
                + "]. JWK: kty=["
                + jwk.getKeyType()
                + "], len=["
                + jwk.size()
                + "], alg=["
                + jwk.getAlgorithm()
                + "], use=["
                + jwk.getKeyUse()
                + "], ops=["
                + jwk.getKeyOperations()
                + "], kid=["
                + jwk.getKeyID()
                + "]."
        );
        final Instant now = Instant.now().truncatedTo(ChronoUnit.SECONDS);
        final SignedJWT unsignedJwt = JwtTestCase.buildUnsignedJwt(
            randomBoolean() ? null : JOSEObjectType.JWT.toString(), 
            randomBoolean() ? null : jwk.getKeyID(), 
            algJwkPair.alg(), 
            randomAlphaOfLengthBetween(10, 20),