$psscriptpath = "C:inetpubhtdocsschool_panelscriptschange.ps1";
    $cmdlet = "powershell.exe -executionpolicy remotesigned -File {$psscriptpath} -username {$username} -password {$password} < NUL";
    echo $cmdlet;
    $output = shell_exec($cmdlet);
    echo $output;

powershell.exe -executionpolicy remotesigned -File C:inetpubhtdocsschool_panelscriptschange.ps1 -username testingacount -password TestingTest321 < NULSet-ADAccountPassword : Access is denied
At C:inetpubhtdocsschool_panelscriptschange.ps1:18 char:22
+ Set-ADAccountPassword <<<<  $username -NewPassword $newpwd -Reset
    + CategoryInfo          : PermissionDenied: (testingacount:ADAccount) [Set-ADAccountPassword], UnauthorizedAccessException
    + FullyQualifiedErrorId : Access is denied,Microsoft.ActiveDirectory.Management.Commands.SetADAccountPassword