<#
=============================================================================================
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

Script Highlights: 
~~~~~~~~~~~~~~~~~
1.The script uses modern authentication to connect to Exchange Online.   
2.The script can be executed with MFA enabled account too.   
3.Exports report results to CSV file.   
4.Allows you to generate an external file access report for a custom period.   
5.Automatically installs the EXO V2 module (if not installed already) upon your confirmation.  
6.The script is scheduler friendly. I.e., Credential can be passed as a parameter instead of saving inside the script. 

For detailed script execution: https://o365reports.com/2021/03/23/audit-external-user-file-access-in-sharepoint-online-using-powershell
============================================================================================
#>
Param
(
    [Parameter(Mandatory = $false)]
    [Nullable[DateTime]]$StartDate,
    [Nullable[DateTime]]$EndDate,
    [string]$AdminName,
    [string]$Password
)

#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
}

#Getting external user file access for past 90 days
if(($StartDate -eq $null) -and ($EndDate -eq $null))
{
 $EndDate=(Get-Date).Date
 $StartDate= ((Get-Date).AddDays(-89)).Date
}
 
#Getting start date for file access report
While($true)
{
 if ($StartDate -eq $null)
 {
  $StartDate=Read-Host Enter start time for report generation '(Eg:03/18/2021)'
 }
 Try
 {
  $Date=[DateTime]$StartDate
  if($Date -gt ((Get-Date).AddDays(-90)))
  { 
   break
  }
  else
  {
   Write-Host `nFile access report can be retrieved only for past 90 days. Please select a date after (Get-Date).AddDays(-90) -ForegroundColor Red
   return
  }
 }
 Catch
 {
  Write-Host `nNot a valid date -ForegroundColor Red
 }
}


#Getting end date for file access report
While($true)
{
 if ($EndDate -eq $null)
 {
  $EndDate=Read-Host Enter End time for File access audit report '(Eg: 03/18/2021)'
 }
 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
 }
}

$OutputCSV=".\ExternalUserFileAccessReport_$((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
}

$AggregateResults = @()
$CurrentResult= @()
$CurrentResultCount=0
$AggregateResultCount=0
Write-Host `nRetrieving external user file access data from $StartDate to $EndDate... -ForegroundColor Yellow
$i=0
$ExportResult=""   
$ExportResults=@()  
while($true)
{ 
 if($CurrentStart -eq $CurrentEnd)
 {
  Write-Host Start and end time are same.Please enter different time range -ForegroundColor Red
  Exit
 }

 #Getting file access audit data for given time range
 $Results=Search-UnifiedAuditLog -StartDate $CurrentStart -EndDate $CurrentEnd -Operations FileAccessed -UserIds *#EXT#* -SessionId s -SessionCommand ReturnLargeSet -ResultSize 5000
 $ResultCount=($Results | Measure-Object).count
 $AllAuditData=@()
 foreach($Result in $Results)
 {
  $i++
  $MoreInfo=$Result.auditdata
  $AuditData=$Result.auditdata | ConvertFrom-Json
  $ActivityTime=Get-Date($AuditData.CreationTime) -format g
  $UserID=$AuditData.userId
  $AccessedFile=$AuditData.SourceFileName
  $FileExtension=$AuditData.SourceFileExtension
  $SiteURL=$AuditData.SiteURL
  $Workload=$AuditData.Workload

  #Export result to csv
  $ExportResult=@{'Accessed Time'=$ActivityTime;'External User'=$UserID;'Workload'=$Workload;'More Info'=$MoreInfo;'Accessed File'=$AccessedFile;'Site URL'=$SiteURL;'File Extension'=$FileExtension}
  $ExportResults= New-Object PSObject -Property $ExportResult  
  $ExportResults | Select-Object 'Accessed Time','External User','Accessed File','Site URL','File Extension','Workload','More Info' | Export-Csv -Path $OutputCSV -Notype -Append 
 }
 Write-Progress -Activity "`n     Retrieving external user file access audit data from $StartDate to $EndDate.."`n" Processed audit record count: $i"
 $currentResultCount=$CurrentResultCount+$ResultCount
 if($CurrentResultCount -eq 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 Agg $AggregateResultCount CurrentResu $CurrentResultCount
   $AggregateResultCount +=$CurrentResultCount
   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($Results.count -lt 5000)
 {
  #$AggregateResults +=$CurrentResult
  $AggregateResultCount +=$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($AggregateResultCount -eq 0)
{
 Write-Host No records found
}
else
{
 Write-Host `nThe output file contains $AggregateResultCount audit records
 if((Test-Path -Path $OutputCSV) -eq "True") 
 {
  Write-Host `n The Output file availble in: -NoNewline -ForegroundColor Yellow
  Write-Host $OutputCSV 
  Write-Host `n~~ Script prepared by AdminDroid Community ~~`n -ForegroundColor Green
  Write-Host "~~ Check out " -NoNewline -ForegroundColor Green; Write-Host "admindroid.com" -ForegroundColor Yellow -NoNewline; Write-Host " to get access to 1800+ Microsoft 365 reports. ~~" -ForegroundColor Green `n`n
  $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 | Out-Null