PutongOJ: unprivileged users can escalate privileges by constructing requests

PutongOJ is online judging software. Prior to version 2.1.0-beta.1, unprivileged users can escalate privileges by constructing requests. This can lead to unauthorized access, enabling users to perform admin-level operations, potentially compromising sensitive data and system integrity. This problem has been fixed in v2.1.0.beta.1. As a workaround, one may apply the patch from commit `211dfe9` manually.