Script to test AD credentials; heavily based on https://gallery.technet.microsoft.com/scriptcenter/Verify-the-Active-021eedea/view/Discussions#content

Test-ADCredential.ps1

#heavily based on https://gallery.technet.microsoft.com/scriptcenter/Verify-the-Active-021eedea/view/Discussions#content
function Test-ADCredential {
    [CmdletBinding()]
    Param
    (
        [Parameter(Mandatory = $true, ValueFromPipeline = $true)]
        [System.Management.Automation.Credential()]
        [System.Management.Automation.PSCredential]$Credential
    )
    begin {
        Add-Type -AssemblyName System.DirectoryServices.AccountManagement
    }
    process {
        if (!($Credential.UserName) -or !($Credential.GetNetworkCredential().Password)) {
            Write-Warning 'Test-ADCredential: Please specify both user name and password'
        } else {
            $DS = [System.DirectoryServices.AccountManagement.PrincipalContext]::new([System.DirectoryServices.AccountManagement.ContextType]::Domain)
            $DS.ValidateCredentials($Credential.UserName, $Credential.GetNetworkCredential().Password) #NB: Username should not contain domain prefix (i.e. use myUsername instead of myDomain\myUsername)
        }
    }
}