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
return null;
        }
        
        if (containsAtLeastTwoDots(userCredentials) == false) {
            return null;
        }
        
        final SignedJWT signedJWT;
        try {
            signedJWT = SignedJWT.parse(userCredentials.toString());
        } catch (ParseException e) {
            logger.debug("Failed to parse JWT bearer token", e);
            return null;
        }
        final JWTClaimsSet jwtClaimsSet;
        try {
            jwtClaimsSet = signedJWT.getJWTClaimsSet();
        } catch (ParseException e) {
            logger.debug("Failed to parse JWT claims set", e);
            return null;
        }
        final SecureString clientCredentials = JwtUtil.getHeaderValue(
            threadContext,
            JwtRealm.HEADER_CLIENT_AUTHENTICATION,
            JwtRealm.HEADER_SHARED_SECRET_AUTHENTICATION_SCHEME,
            true
        );
        
        
        final String issuer = jwtClaimsSet.getIssuer();