Microsoft Teams external domain whitelisting

#Prerequisites :
# Update-Module MicrosoftTeams -RequiredVersion 5.5

Disconnect-MgGraph
Connect-MgGraph -Scopes "user.read.all"

[array]$Guests = Get-MgUser -All -Filter "usertype eq 'Guest'"
Write-Host ("{0} guest accounts found" -f $Guests.Count)
$GuestList = [System.Collections.Generic.List[Object]]::new()

ForEach ($Guest in $Guests) {
    $Domain = $Guest.Mail.Split("@")[1]
    $ReportLine = [PSCustomObject][Ordered]@{
      Guest    = $Guest.Mail
      Domain   = $Domain
      Name     = $Guest.DisplayName }
    $GuestList.Add($ReportLine)
}
Write-Host ""
Write-Host "Guest accounts found for the following domains"
Write-Host "----------------------------------------------"
$GuestList | Group-Object Domain | Sort-Object Name | Select-Object Name, Count
$Domains = $GuestList | Sort-Object Domain -Unique | Select-Object -ExpandProperty Domain

Write-Host "Connecting to Microsoft Teams to check current external access configuration"

Disconnect-MicrosoftTeams
Connect-MicrosoftTeams

# Get current set of domains configured for Teams extrenal access
$DomainConfiguration  = Get-CsTenantFederationConfiguration  | Select-Object -ExpandProperty AllowedDomains
# Check the set of domains that aren't in the current configuration
[array]$DomainsToAdd = $Domains | Where-Object {$_ -notin $DomainConfiguration.AllowedDomain.Domain}

$Prompt = "Do you want to add the following domains to the list allowed for Teams external access? " + $DomainsToAdd -join ", "
$Choice = Read-Host $Prompt

#Type Y to add detected domains
If (($Choice.ToUpper()) -eq "Y") {
        $AllList = new-object object[] $DomainsToAdd.Count
        $i = 0

        ForEach ($Domain in $DomainsToAdd) {
         $x = New-CsEdgeDomainPattern -Domain $Domain
         $AllList[$i] = $x
         $i++
        }

        $newAllowList = New-CsEdgeAllowList -AllowedDomain @($AllList)
        # replace the current domains list for the new list generated above
        Set-CsTenantFederationConfiguration -AllowedDomains $newAllowList
    }

$DomainConfiguration  = Get-CsTenantFederationConfiguration  | Select-Object -ExpandProperty AllowedDomains
Write-Host ("External access for Teams now includes {0} domains" -f $DomainConfiguration.AllowedDomain.Domain.count)