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/main/java/org/elasticsearch/xpack/security/authc/jwt/JwtRealm.java
|| value instanceof Boolean
            || value instanceof Number
            || (value instanceof Collection
                && ((Collection<?>) value).stream().allMatch(e -> e instanceof String || e instanceof Boolean || e instanceof Number)));
    }
    
    record ExpiringUser(User user, Date exp) {
        ExpiringUser {
            Objects.requireNonNull(user, "User must not be null");
            Objects.requireNonNull(exp, "Expiration date must not be null");
        }
    }
    /**
     * This is a lightweight pre-check for the JWT token format.
     * If this returns {@code true}, the token MIGHT be a JWT. Otherwise, the token is definitely not a JWT.
     */
    private static boolean containsAtLeastTwoDots(SecureString secureString) {
        if (secureString == null || secureString.length() < 2) {
            return false;
        }
        int ndots = 0;
        for (int i = 0; i < secureString.length(); i++) {
            if (secureString.charAt(i) == '.' && ++ndots >= 2) {
                return true;
            }
        }
        return false;
    }
}