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
final ThreadContext tc6 = createThreadContext("Head.Body.Sig", clientSecret);
        assertThat(jwtIssuerAndRealm.realm().token(tc6), nullValue());
        
        final SignedJWT parsedJwt = SignedJWT.parse(jwt.toString());
        final JWSHeader validHeader = parsedJwt.getHeader();
        final JWTClaimsSet validClaimsSet = parsedJwt.getJWTClaimsSet();
        final Base64URL validSignature = parsedJwt.getSignature();
        {   
            final SecureString unsignedJwt = new SecureString(new PlainJWT(validClaimsSet).serialize().toCharArray());
            final ThreadContext tc = createThreadContext(unsignedJwt, clientSecret);
            assertThat(jwtIssuerAndRealm.realm().token(tc), nullValue());
        }
        {   
            final String mixupAlg; 
            if (JwtRealmSettings.SUPPORTED_SIGNATURE_ALGORITHMS_HMAC.contains(validHeader.getAlgorithm().getName())) {
                if (JwtRealmInspector.getJwksAlgsPkc(jwtIssuerAndRealm.realm()).algs().isEmpty()) {
                    mixupAlg = null; 
                } else {
                    mixupAlg = randomFrom(JwtRealmInspector.getJwksAlgsPkc(jwtIssuerAndRealm.realm()).algs()); 
                }
            } else {
                if (JwtRealmInspector.getJwksAlgsHmac(jwtIssuerAndRealm.realm()).algs().isEmpty()) {
                    mixupAlg = null; 
                } else {
                    mixupAlg = randomFrom(JwtRealmInspector.getJwksAlgsHmac(jwtIssuerAndRealm.realm()).algs()); 
                }
            }
            
            if (Strings.hasText(mixupAlg)) {
                final JWSHeader tamperedHeader = new JWSHeader.Builder(JWSAlgorithm.parse(mixupAlg)).build();