[stable31] fix: Check that user actually can validate password for js

[backportbot]

Backport of PR #50465

[dansmolik]

Sorry guys is fix included in current 31.0.4 ? Thanks for info.

[AndyScherzinger]

Hi @dansmolik no, will ship with the next release 15th May 2025.

[ghnfox509]

I was experiencing this issue on 31.0.4 which I freshly installed yesterday, and after updating to 31.0.5 a few minutes ago the issue is still there (cannot add external storage, asks me for password and says the password is wrong every time when it is not, I do have LDAP enabled however am using the local nextcloud admin account to make these changes). I don't use git much myself but I do notice in the pull request there seems to be 2 files that were unchanged due to being tainted ? maybe the full fix did not get in because of that? (UPDATE: worked around the issue by exporting the rows of config from my owncloud and imported them to nextcloud for external storage, works fine now)