Due to a change in cryptography, an upgrade to Sitecore 10 may lock some of your users, making their passwords to stop working.
The easiest way to solve this would be create a Powershell Script to reset their password
I had to create a small powershell to perform this task
The script below will reset the users within domain “sitecore” and print their result on the screen
Write-Host "Starting script for reset all the users under sitecore domain"
[int]$passlength = 8
[string]$pass
$users = Get-User -Filter "sitecore\*"
$i = 1;
ForEach ($item in $users) {
for($i=0; $i -lt $passlength; $i++)
{
$pass += [char](Get-Random -Minimum 33 -Maximum 126)
}
Set-UserPassword -Identity $item.LocalName -NewPassword $pass -Reset
Write-Host "Username,"$item.LocalName","$item.Name",Password,"$pass
$pass = ""
}
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