Bug#1042824: Logging into SLBackup frontend returns error

[Guido Berhoerster]

There are actually two critical problems causing logins to fail:

1. usage of crypt() without a salt (not actually used for passwords
   but as a hash function for some homemade encryption, see
   https://salsa.debian.org/debian-edu-pkg-team/slbackup-php/-/blob/8eb0d468422cb3e06eed0092643d1bb4082f9b1c/src/index.php#L698)
2. a typo where the key is switched with the value while looping over
   an associative array which causes an exception with PHP 8 since 
   the key is a string accessed as an associative array (see
   https://salsa.debian.org/debian-edu-pkg-team/slbackup-php/-/blob/8eb0d468422cb3e06eed0092643d1bb4082f9b1c/src/index.php#L48)

-- 
Guido Berhoerster