Add input sanitization to prevent injection and XSS attacks (Issue #700)

[anshul23102]

Summary

Sanitize username and email inputs in auth validator to remove potentially dangerous characters and injection patterns. This prevents malicious payloads from being stored in the database and protects against XSS and injection attacks.

Changes

• Add sanitizeString function that removes HTML tags and script patterns
• Apply sanitization transform to username and email fields in schemas
• Remove dangerous characters like <>, quotes, semicolons
• Strip javascript: protocol and event handler patterns

Testing

1. Attempt to sign up with username containing HTML tags (e.g., '<script>alert("xss")</script>')
2. Verify username is stored without tags
3. Attempt email with injection patterns (e.g., '')
4. Verify email is sanitized
5. Verify legitimate usernames/emails with special chars still work as intended

Type of Change

• Security fix

Contributor Declaration

This contribution is original work and I have the right to contribute this code to the project. I understand that the project is licensed under its respective license and my contributions will be available under the same license terms.

Closes #700

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📥 Commits

Reviewing files that changed from the base of the PR and between 53f820b and bd0618f.

📒 Files selected for processing (1)

• backend/validators/authValidator.js

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🧪 Generate unit tests (beta)

• Create PR with unit tests

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[anshul23102]

Could the maintainers please add relevant labels to this PR? Suggested labels:

• gssoc:approved
• type:security
• severity:high
• area:security

This would help with issue tracking and organization. Thank you!