CVE-2021-31404: Timing side channel vulnerability in UIDL request handler in Vaadin 10, 11-14, and 15-18

The vulnerability manifests in security token comparisons using String.equals() which leaks timing information. The patches explicitly modify three comparison points across different handlers (CSRF, push ID, and upload security) to use constant-time MessageDigest.isEqual. The original unpatched versions of these functions would appear in runtime profiles during token validation when processing malicious requests. Each identified function directly handles security-critical comparisons and shows clear evidence of insecure pre-patch implementations in the provided diffs.