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/JwtRealmAuthenticateTests.java
if (racingCountDown.await(10, TimeUnit.SECONDS)) {
                            for (int j = 0; j < 10; j++) {
                                jwtIssuerAndRealm.realm().processValidatedJwt("token-principal", jwtCacheKey, validClaimsSet, future);
                                assertThat(future.actionGet().getValue().principal(), equalTo(user.principal()));
                            }
                            completionCountDown.countDown();
                        } else {
                            throw new AssertionError("Racing is not ready within the given time period");
                        }
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                });
            }
            threads[i].start();
        }
        if (threadsCountDown.await(10, TimeUnit.SECONDS)) {
            racingCountDown.countDown();
        } else {
            throw new AssertionError("Threads are not ready within the given time period");
        }
        if (false == completionCountDown.await(30, TimeUnit.SECONDS)) {
            throw new AssertionError("Test is not completed in time, check whether threads had deadlock");
        }
        for (Thread thread : threads) {
            thread.join();
        }
    }
}