OpenVPN: Username as CN depends on authmode being set

[swhite2]

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Describe the bug

If enabling Username as CN while leaving Authentication empty, OpenVPN will refuse to start, since there is no authentication, there will also not be a username to match on.

To Reproduce

Steps to reproduce the behavior:

1. Create an OpenVPN instance
2. Enable Username as CN
3. Do not set any Authentication
4. Start OpenVPN, see error in log:

--username-as-common-name must be used with --management-client-auth, an --auth-user-pass-verify script, or plugin

Core only uses auth-user-pass-verify.

Expected behavior

Validation error if no Authentication set while Username as CN is enabled.

Describe alternatives you considered

N/A

Screenshots

N/A

Relevant log files

N/A

Additional context

N/A

Environment

OPNsense 26.7.a_180 (amd64).