[Feature]: Support for dry-run

[k0ste]

Motivation

It will be nice to have ability for a dry-run configuration

With a --dry-run option is possible to verify the config before restart application
How this should work:

[root@host]# oauth2-proxy --config /etc/oauth2-proxy/oauth2-proxy.conf --dry-run
[2024/05/13 19:47:00] [main.go:52] invalid configuration:
  cookie_secret must be 16, 24, or 32 bytes to create an AES cipher, but is 28 bytes

Exit code should be not zero

As we can see, if administrator, or orchestrator tool restart the application, the service goes down. With dry-run feature, config may be validated before application restart

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Examples of application that already implemented dry-run feature:

• sshd -T -f %s
• keepalived -t -f %s
• nginx -t -c %s

Possible solution

No response

Provider

None