Added User certificate mode as the default mode

[RezaT4795]

• Added User certificate mode as the default mode
• password mode for fallback
• enable/disable user certificates

[gemini-code-assist]

Summary of Changes

Hello @RezaT4795, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the security and manageability of the ocserv VPN server by implementing user certificate authentication as the default method, while still providing password authentication as a fallback. It introduces a robust set of command-line tools for managing user certificates, including their creation, revocation, and temporary suspension, alongside comprehensive Certificate Revocation List (CRL) handling. This upgrade streamlines the process of deploying and maintaining a more secure VPN environment.

Highlights

• Default Certificate Authentication: ocserv is now configured to prioritize user certificate authentication as the primary method.
• Password Fallback: Password-based authentication is maintained as a secondary, fallback mechanism for user access.
• Enhanced User Management: New command-line tools are introduced for comprehensive management of user certificates, including their creation, listing, deletion, temporary suspension, and re-enabling.
• CRL Integration: Certificate Revocation List (CRL) generation and management are now integrated, ensuring that revoked or suspended certificates are properly handled for enhanced security.
• Script Version Update: The script version has been updated to 2.0.0, reflecting the significant new features and improvements in user and certificate management.

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[gemini-code-assist]

Code Review

This pull request introduces a major feature: certificate-based authentication with a password fallback. The changes are extensive and well-structured, refactoring user management into a more robust system that handles both certificates and passwords.

My review focuses on several key areas:

• Security: I've identified a critical directory traversal vulnerability due to unsanitized username input and suggested validation. I also found an issue with grep patterns that could lead to incorrect user matching.
• Code Quality: I've suggested refactoring the way functions pass data to each other, moving from a confusing here-document approach to standard function arguments. This will improve readability and maintainability.
• Consistency: I've pointed out minor inconsistencies, such as dead code in one script and a copy-pasted prompt in another.

Overall, this is a great enhancement. Addressing these points will make the script more secure and robust.