Cannot access SharePoint online _layouts pages using powershell

Question

Would appreciate some help here.

Using the following powershell code I can access all Sharepoint online web pages but for any page containing _layouts I get:

Exception calling "DownloadString" with "1" argument(s): "The remote server returned an error: (401) Unauthorized."

I am using an admin account.

What setting do I need to change to access these pages via this method?

$webClient = New-Object System.Net.WebClient 
$webClient.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($username, $securePassword) 
$webClient.Headers.Add("X-FORMS_BASED_AUTH_ACCEPTED", "f")
$HTML = $webClient.DownloadString($cloudUrl)

Answer 1

If you want to get version history of list items in SharePoint Online, the following PowerShell script for your reference.

#Load SharePoint CSOM Assemblies
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.dll"
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.Runtime.dll"

Function Export-VersionHistory()
{
  param
    (
        [Parameter(Mandatory=$true)] [string] $SiteURL,
        [Parameter(Mandatory=$true)] [string] $ListName,
        [Parameter(Mandatory=$true)] [string] $CSVFile
    )
    Try {

        #Delete the Output report file if exists
        if (Test-Path $CSVFile) { Remove-Item $CSVFile }

        #Get Credentials to connect
        $Cred= Get-Credential
        $Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.Username, $Cred.Password)

        #Setup the context
        $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
        $Ctx.Credentials = $Credentials

        #Get the List
        $List = $Ctx.Web.Lists.GetByTitle($ListName)
        $Ctx.Load($List)
        $Ctx.ExecuteQuery()

        #Get all items
        $Query = [Microsoft.SharePoint.Client.CamlQuery]::CreateAllItemsQuery()
        $ListItems = $List.GetItems($Query)
        $Ctx.Load($ListItems)
        $Ctx.ExecuteQuery()

        #Array to hold result
        $VersionHistoryData = @()

        #Iterate throgh each item
        Foreach ($Item in $ListItems)
        {
            write-host "Processing Item:" $item.id -f Yellow

            #Get all versions of the list item
            $Versions = $Item.versions
            $ctx.Load($Versions)
            $Ctx.ExecuteQuery()

            If($Versions.count -gt 0)
            {
                #Iterate each version
                Foreach($Version in $Versions)
                {
                    #Get the Creator object of the version
                    $CreatedBy =  $Version.createdby
                    $Ctx.Load($CreatedBy)
                    $Ctx.ExecuteQuery()

                    #Send Data to object array
                    $VersionHistoryData += New-Object PSObject -Property @{
                    'Item ID' = $Item.ID
                    'Title' =  $Version.FieldValues["Title"]
                    'Version Label' = $Version.VersionLabel
                    'Version ID' = ($Version.VersionId/512)
                    'Created On' = (Get-Date ($Version.Created) -Format "yyyy-MM-dd/HH:mm:ss")
                    'Created By' = $CreatedBy.Email
                    }
                }
            }
        }

        #Export the data to CSV
        $VersionHistoryData | Export-Csv $CSVFile -Append -NoTypeInformation

        write-host -f Green "Version History Exported Successfully to:" $CSVFile
     }
    Catch {
        write-host -f Red "Error Exporting version History to CSV!" $_.Exception.Message
    }
}

#Set parameter values
$SiteURL="https://tenant.sharepoint.com/sites/lz"
$ListName="CustomList"
$CSVFile="C:\Temp\VersionHistory.csv"

#Call the function to generate version History Report
Export-VersionHistory -SiteURL $SiteURL -ListName $ListName -CSVFile $CSVFile

Note: Download the latest CSOM library for SharePoint Online.