Code review improvements

Security audit reveals potential vulnerabilities. Need to review authentication flows, input validation, and data sanitization.

Start by reviewing the repository's authentication flows, input validation, and data sanitization areas, since the issue does not name specific files or tests. Confirm the vulnerabilities identified by the security audit and define the affected behaviors before making changes. Done should mean the identified vulnerabilities are addressed and the relevant security checks pass.

Written by the indexing model from the issue text.