Add occ command for checking the password for a given user ID.

[stellarpower]

• Resolves: https://help.nextcloud.com/t/check-credentials-programatically-server-side/185703

Summary

Adds an occ command for checking the password for the given user ID. The user can provide the password literally in the CLI arguments (less secure but other applications don't prevent this), using OC_PASS, through stdin or interactively.

I have a small self-contained application that needs to authenticate users. Rather than maintain a separate set of credentials, or set up something like LDAP (would be overkill), adding a command like this seems the best way to achieve what I needed - the application is server-side and can then look up the user and password, and the exit status is used to determine if the user was authenticated or not.

Uploading so that the community can benefit from contributions, but please do feel free to pull into a feature branch and rework or modify heavily and use as a springboard. This solved a particular usecase I had so figured may be useful.

TODO

• Tried to make the interactive prompt detect if it's in a TTY or a pipe, but this seems to return true in either case
• People may want to modify this heavily or not add it for security implications for what code is in here. I've thought about some basics, but am not a security expert, nor do I know much about nextcloud's design. I started from the password reset command; so this seems comparable, but someone should review and consider the implications
• I'm by no means a PHP developer, so there may be significant defects.
• Don't have the ability to test against current master; slight modifications and it appears to work on my installed server, running NC 21, but would need to be tested properly against master code.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)