<#
=============================================================================================
Name:           Office 365 external user file access report
Description:    This script exports SharePoint Online external user file access report to CSV
Version:        1.0
Website:        o365reports.com
Script by:      O365Reports Team
For detailed script execution: https://o365reports.com/2021/05/20/audit-sharepoint-online-external-sharing-using-powershell
============================================================================================
#>

Param
(
    [Parameter(Mandatory = $false)]
    [Nullable[DateTime]]$StartDate,
    [Nullable[DateTime]]$EndDate,
    [switch]$SharePointOnline,
    [switch]$OneDrive,
    [string]$AdminName,
    [string]$Password
)

Function Connect_Exo
{
 #Check for EXO v2 module inatallation
 $Module = Get-Module ExchangeOnlineManagement -ListAvailable
 if($Module.count -eq 0) 
 { 
  Write-Host Exchange Online PowerShell V2 module is not available  -ForegroundColor yellow  
  $Confirm= Read-Host Are you sure you want to install module? [Y] Yes [N] No 
  if($Confirm -match "[yY]") 
  { 
   Write-host "Installing Exchange Online PowerShell module"
   Install-Module ExchangeOnlineManagement -Repository PSGallery -AllowClobber -Force
  } 
  else 
  { 
   Write-Host EXO V2 module is required to connect Exchange Online.Please install module using Install-Module ExchangeOnlineManagement cmdlet. 
   Exit
  }
 } 
 Write-Host Connecting to Exchange Online...
 #Storing credential in script for scheduling purpose/ Passing credential as parameter - Authentication using non-MFA account
 if(($AdminName -ne "") -and ($Password -ne ""))
 {
  $SecuredPassword = ConvertTo-SecureString -AsPlainText $Password -Force
  $Credential  = New-Object System.Management.Automation.PSCredential $AdminName,$SecuredPassword
  Connect-ExchangeOnline -Credential $Credential
 }
 else
 {
  Connect-ExchangeOnline
 }
}

$MaxStartDate=((Get-Date).AddDays(-89)).Date

#Getting external user file access for past 90 days
if(($StartDate -eq $null) -and ($EndDate -eq $null))
{
 $EndDate=(Get-Date).Date
 $StartDate=$MaxStartDate
}
$startDate
#Getting start date to generate external sharing report
While($true)
{
 if ($StartDate -eq $null)
 {
  $StartDate=Read-Host Enter start time for report generation '(Eg:04/28/2021)'
 }
 Try
 {
  $Date=[DateTime]$StartDate
  if($Date -ge $MaxStartDate)
  { 
   break
  }
  else
  {
   Write-Host `nExternal sharing report can be retrieved only for past 90 days. Please select a date after $MaxStartDate -ForegroundColor Red
   return
  }
 }
 Catch
 {
  Write-Host `nNot a valid date -ForegroundColor Red
 }
}


#Getting end date to generate external sharing report
While($true)
{
 if ($EndDate -eq $null)
 {
  $EndDate=Read-Host Enter End time for report generation '(Eg: 04/28/2021)'
 }
 Try
 {
  $Date=[DateTime]$EndDate
  if($EndDate -lt ($StartDate))
  {
   Write-Host End time should be later than start time -ForegroundColor Red
   return
  }
  break
 }
 Catch
 {
  Write-Host `nNot a valid date -ForegroundColor Red
 }
}

$OutputCSV=".\ExternalSharingReport_$((Get-Date -format yyyy-MMM-dd-ddd` hh-mm` tt).ToString()).csv" 
$IntervalTimeInMinutes=1440    #$IntervalTimeInMinutes=Read-Host Enter interval time period '(in minutes)'
$CurrentStart=$StartDate
$CurrentEnd=$CurrentStart.AddMinutes($IntervalTimeInMinutes)

#Check whether CurrentEnd exceeds EndDate
if($CurrentEnd -gt $EndDate)
{
 $CurrentEnd=$EndDate
}

if($CurrentStart -eq $CurrentEnd)
{
 Write-Host Start and end time are same.Please enter different time range -ForegroundColor Red
 Exit
}

Connect_EXO
$AggregateResults = @()
$CurrentResult= @()
$CurrentResultCount=0
$AggregateResultCount=0
Write-Host `nRetrieving external sharing events from $StartDate to $EndDate...
$ProcessedAuditCount=0
$OutputEvents=0
$ExportResult=""   
$ExportResults=@()  

while($true)
{ 
 #Getting exteranl sharing audit data for given time range
 $Results=Search-UnifiedAuditLog -StartDate $CurrentStart -EndDate $CurrentEnd -Operations "Sharinginvitationcreated,AnonymousLinkcreated,AddedToSecureLink" -SessionId s -SessionCommand ReturnLargeSet -ResultSize 5000
 $ResultCount=($Results | Measure-Object).count
 foreach($Result in $Results)
 {
  $ProcessedAuditCount++
  $MoreInfo=$Result.auditdata
  $Operation=$Result.Operations
  $AuditData=$Result.auditdata | ConvertFrom-Json
  $Workload=$AuditData.Workload

  #Filter for SharePointOnline external Sharing events
  If($SharePointOnline.IsPresent -and ($Workload -eq "OneDrive"))
  {
   continue
  }

  If($OneDrive.IsPresent -and ($Workload -eq "SharePoint"))
  {
   continue
  }
  
  #Check for Guest sharing
  if($Operation -ne "AnonymousLinkcreated")
  {
   If($AuditData.TargetUserOrGroupType -ne "Guest")
   {
    continue
   }
   $SharedWith=$AuditData.TargetUserOrGroupName
  }
  else
  {
   $SharedWith="Anyone with the link can access"
  }

  $ActivityTime=Get-Date($AuditData.CreationTime) -format g
  $SharedBy=$AuditData.userId
  $SharedResourceType=$AuditData.ItemType
  $sharedResource=$AuditData.ObjectId
  $SiteURL=$AuditData.SiteURL
  

  #Export result to csv
  $OutputEvents++
  $ExportResult=@{'Shared Time'=$ActivityTime;'Sharing Type'=$Operation;'Shared By'=$SharedBy;'Shared With'=$SharedWith;'Shared Resource Type'=$SharedResourceType;'Shared Resource'=$SharedResource;'Site url'=$Siteurl;'Workload'=$Workload;'More Info'=$MoreInfo}
  $ExportResults= New-Object PSObject -Property $ExportResult  
  $ExportResults | Select-Object 'Shared Time','Shared By','Shared With','Shared Resource Type','Shared Resource','Site URL','Sharing Type','Workload','More Info' | Export-Csv -Path $OutputCSV -Notype -Append 
 }
 Write-Progress -Activity "`n     Retrieving external sharing events from $CurrentStart to $CurrentEnd.."`n" Processed audit record count: $ProcessedAuditCount"
 $currentResultCount=$CurrentResultCount+$ResultCount
 if($CurrentResultCount -ge 50000)
 {
  Write-Host Retrieved max record for current range.Proceeding further may cause data loss or rerun the script with reduced time interval. -ForegroundColor Red
  $Confirm=Read-Host `nAre you sure you want to continue? [Y] Yes [N] No
  if($Confirm -match "[Y]")
  {
   Write-Host Proceeding audit log collection with data loss
   [DateTime]$CurrentStart=$CurrentEnd
   [DateTime]$CurrentEnd=$CurrentStart.AddMinutes($IntervalTimeInMinutes)
   $CurrentResultCount=0
   $CurrentResult = @()
   if($CurrentEnd -gt $EndDate)
   {
    $CurrentEnd=$EndDate
   }
  }
  else
  {
   Write-Host Please rerun the script with reduced time interval -ForegroundColor Red
   Exit
  }
 }

 
 if($Results.count -lt 5000)
 {
  #$AggregateResultCount +=$CurrentResultCount
  if($CurrentEnd -eq $EndDate)
  {
   break
  }
  $CurrentStart=$CurrentEnd 
  if($CurrentStart -gt (Get-Date))
  {
   break
  }
  $CurrentEnd=$CurrentStart.AddMinutes($IntervalTimeInMinutes)
  $CurrentResultCount=0
  $CurrentResult = @()
  if($CurrentEnd -gt $EndDate)
  {
   $CurrentEnd=$EndDate
  }
 }
}

If($OutputEvents -eq 0)
{
 Write-Host No records found
}
else
{
 Write-Host `nThe output file contains $OutputEvents audit records
 if((Test-Path -Path $OutputCSV) -eq "True") 
 {
  Write-Host `nThe Output file availble in $OutputCSV -ForegroundColor Green
  $Prompt = New-Object -ComObject wscript.shell   
  $UserInput = $Prompt.popup("Do you want to open output file?",`   
 0,"Open Output File",4)   
  If ($UserInput -eq 6)   
  {   
   Invoke-Item "$OutputCSV"   
  } 
 }
}

#Disconnect Exchange Online session
Disconnect-ExchangeOnline -Confirm:$false -InformationAction Ignore -ErrorAction SilentlyContinue