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 JWTClaimsSet claimsSet = new JWTClaimsSet.Builder(validClaimsSet).notBeforeTime(future).build();
            final SecureString jwtIatFuture = signJwt(algJwkPair.jwk(), new SignedJWT(jwtHeader, claimsSet));
            verifyAuthenticateFailureHelper(jwtIssuerAndRealm, jwtIatFuture, clientSecret);
        }
        {   
            final JWTClaimsSet claimsSet = new JWTClaimsSet.Builder(validClaimsSet).expirationTime(past).build();
            final SecureString jwtExpPast = signJwt(algJwkPair.jwk(), new SignedJWT(jwtHeader, claimsSet));
            verifyAuthenticateFailureHelper(jwtIssuerAndRealm, jwtExpPast, clientSecret);
        }
    }
    /**
     * Configure two realms for same issuer. Use identical realm config, except different client secrets.
     * Generate a JWT which is valid for both realms, but verify authentication only succeeds for second realm with correct client secret.
     * @throws Exception Unexpected test failure
     */
    public void testSameIssuerTwoRealmsDifferentClientSecrets() throws Exception {
        final int realmsCount = 2;
        final List<Realm> allRealms = new ArrayList<>(realmsCount); 
        final JwtIssuer jwtIssuer = createJwtIssuer(0, 12, 1, 1, 1, false);
        printJwtIssuer(jwtIssuer);
        jwtIssuerAndRealms = new ArrayList<>(realmsCount);
        for (int i = 0; i < realmsCount; i++) {
            final String realmName = "realm_" + jwtIssuer.issuerClaimValue + "_" + i;
            final String clientSecret = "clientSecret_" + jwtIssuer.issuerClaimValue + "_" + i;
            final Settings.Builder authcSettings = Settings.builder()
                .put(globalSettings)
                .put(RealmSettings.getFullSettingKey(realmName, JwtRealmSettings.ALLOWED_ISSUER), jwtIssuer.issuerClaimValue)
                .put(
                    RealmSettings.getFullSettingKey(realmName, JwtRealmSettings.ALLOWED_SIGNATURE_ALGORITHMS),
                    String.join(",", jwtIssuer.algorithmsAll)