Check if user password input is valid in Powershell script

I have this in my library:

$cred = Get-Credential #Read credentials
 $username = $cred.username
 $password = $cred.GetNetworkCredential().password

 # Get current domain using logged-on user's credentials
 $CurrentDomain = "LDAP://" + ([ADSI]"").distinguishedName
 $domain = New-Object System.DirectoryServices.DirectoryEntry($CurrentDomain,$UserName,$Password)

if ($domain.name -eq $null)
{
 write-host "Authentication failed - please verify your username and password."
 exit #terminate the script.
}
else
{
 write-host "Successfully authenticated with domain $domain.name"
}

This is what I've used in the past; it's supposed to work for local machine accounts and 'application directory', but so far I've only used it successfully with AD credentials:

    function Test-Credential {
    <#
    .SYNOPSIS
        Takes a PSCredential object and validates it against the domain (or local machine, or ADAM instance).

    .PARAMETER cred
        A PScredential object with the username/password you wish to test. Typically this is generated using the Get-Credential cmdlet. Accepts pipeline input.

    .PARAMETER context
        An optional parameter specifying what type of credential this is. Possible values are 'Domain','Machine',and 'ApplicationDirectory.' The default is 'Domain.'

    .OUTPUTS
        A boolean, indicating whether the credentials were successfully validated.

    #>
    param(
        [parameter(Mandatory=$true,ValueFromPipeline=$true)]
        [System.Management.Automation.PSCredential]$credential,
        [parameter()][validateset('Domain','Machine','ApplicationDirectory')]
        [string]$context = 'Domain'
    )
    begin {
        Add-Type -assemblyname system.DirectoryServices.accountmanagement
        $DS = New-Object System.DirectoryServices.AccountManagement.PrincipalContext([System.DirectoryServices.AccountManagement.ContextType]::$context) 
    }
    process {
        $DS.ValidateCredentials($credential.UserName, $credential.GetNetworkCredential().password)
    }
}

I've found this post useful however it didn't solve my problem as I was trying to run it from a script with the local admin account logged on. It does not seem to work as local admin (only when logged on as a domain user).

However I did finally manage to get a working solution and since it was so much trouble I thought I'd share it here so anyone else with this problem will have the answer right here. Both answers on the one page depending on your needs.

Note that higher up in the scipt (not included here as this is just the get-credentials section) powergui is installed and is a requirement for this code below (as well as the "Add-PSSnapin Quest.ActiveRoles.ADManagement" line). Not sure what powergui does that's different but no one else could tell me and it works.

Subsitute your own domain name in the "domain_name" sections.

#Get credentials
$credential_ok = 0
while ($credential_ok -ne 1)
{
    $credential = get-credential
    $result = connect-qadservice -service *domain_name* -credential $credential
    [string]$result_string = $result.domain
    if ($result_string -eq "*domain_name*")
    {
        $credential_ok = 1
        #authenticated
    }
    else
    {
        #failed
    }     
}
$username = $credential.username 
$password = $credential.GetNetworkCredential().password 

$date = get-date
Add-Content "c:\lbin\Install_log.txt" "Successfully authenticated XP script as $username $date"

(yet) Another version:

param([string]$preloadServiceAccountUserName = "")

function HarvestCredentials()
{

        [System.Management.Automation.PSCredential]$credentialsOfCurrentUser = Get-Credential -Message "Please enter your username & password" -UserName $preloadServiceAccountUserName

        if ( $credentialsOfCurrentUser )
        {
            $credentialsOfCurrentUser = $credentialsOfCurrentUser
        }
        else
        {
            throw [System.ArgumentOutOfRangeException] "Gui credentials not entered correctly"          
        }

    Try
    {


        # see https://msdn.microsoft.com/en-us/library/system.directoryservices.directoryentry.path(v=vs.110).aspx
        # validate the credentials are legitimate
        $validateCredentialsTest = (new-object System.DirectoryServices.DirectoryEntry ("WinNT://"+$credentialsOfCurrentUser.GetNetworkCredential().Domain), $credentialsOfCurrentUser.GetNetworkCredential().UserName, $credentialsOfCurrentUser.GetNetworkCredential().Password).psbase.name
        if ( $null -eq  $validateCredentialsTest)
        {
            throw [System.ArgumentOutOfRangeException] "Credentials are not valid.  ('" + $credentialsOfCurrentUser.GetNetworkCredential().Domain + '\' + $credentialsOfCurrentUser.GetNetworkCredential().UserName + "')"
        }
        else
        {
            $t = $host.ui.RawUI.ForegroundColor
            $host.ui.RawUI.ForegroundColor = "Magenta"
            Write-Output "GOOD CREDENTIALS"
            $host.ui.RawUI.ForegroundColor = $t
        }
    }
    Catch
    {

        $ErrorMessage = $_.Exception.Message
        $FailedItem = $_.Exception.ItemName
        $StackTrace = $_.Exception.StackTrace

        $t = $host.ui.RawUI.ForegroundColor
        $host.ui.RawUI.ForegroundColor = "Red"

        Write-Output "Exception - $ErrorMessage"
        Write-Output "Exception - $FailedItem"
        Write-Output "Exception - $StackTrace"

        $host.ui.RawUI.ForegroundColor = $t

        throw [System.ArgumentOutOfRangeException] "Attempt to create System.DirectoryServices.DirectoryEntry failed.  Most likely reason is that credentials are not valid."
    }

}


Try
{

    HarvestCredentials

}
Catch
{
    $ErrorMessage = $_.Exception.Message
    $FailedItem = $_.Exception.ItemName
    $StackTrace = $_.Exception.StackTrace

    $t = $host.ui.RawUI.ForegroundColor
    $host.ui.RawUI.ForegroundColor = "Red"

    Write-Output "Exception - " + $ErrorMessage
    Write-Output "Exception - " + $FailedItem
    Write-Output "Exception - " + $StackTrace

    $host.ui.RawUI.ForegroundColor = $t

    Break
}
Finally
{
    $Time=Get-Date
    Write-Output "Done - " + $Time
}

and

.\TestCredentials.ps1 -preloadServiceAccountUserName "mydomain\myusername"