How to use Office 365 Service Communications API V2 with PowerShell

Below is the PowerShell script I came up with which uses v2 of the Graph API.  A few notes:

• You will need to register an Azure app for use with this script.  The app will need to be granted permissions to read tenant health info.  I have not included instructions for registering the Azure app.  A good starting point on how to do this can be found at the following URL: https://lazyadmin.nl/it/using-microsoft-graph-api-with-powershell/. 
• Review the "script variables" section of the script and adjust as necessary.
• As this is my first try at using the Graph API, I'm not convinced the portion of the code which retrieves the OAuth token is optimal.  Please share any changes you make to improve that portion of the script.
• The secret for the registered app is stored in a file (location specified in PassFile variable).  For the version of the script we use, we encrypt PassFile and have the script decrypt it in order to retrieve the secret.  For the version I've attached I assume an unencrypted file is used to store the secret.

Hopefully others can make use of this and please share any improvements you make with the community. 

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Monitor-Tenant-Health

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#Script variables
$HistoryFile = "Enter folder and path to file which will be used to track tenant health history (i.e. C:\Temp\TenantHealth.csv)"
$PassFile = "Location of file containing client secret for Azure app created for use in obtaining tenant health"
$ClientID = "Application ID of Azure app created for use in obtaining tenant health"
$TenantDomain = "yourtenant.onmicrosoft.com"
$TenantGUID = "GUID of your tenant"
$NotificationRecipients = @("someone@somewhere.com")
$NotificationSender = "donotreply@somewhere.com"
$SmtpServer = "smtpserver.somewhere.com"
$SmtpPort = "25"
$RedirectUri = "https://localhost"
$LoginUrl = "https://login.microsoft.com"
$Resource = "https://manage.office.com"

#Retrieve health events from previous run
$HistoryTable = @{}
If (Test-Path $HistoryFile)
{
$HistoryFileContents = Get-Content -Path $HistoryFile
ForEach ($Entry in $HistoryFileContents) {$HistoryTable.Add(($Entry.Split(","))[0],($Entry.Split(","))[1])}
}

#Retrieve OAuth token
$ClientSecret = Get-Content $PassFile
$RequestBody = @{grant_type="client_credentials";redirect_uri=$RedirectUri;resource=$Resource;client_id=$ClientID;client_secret=$ClientSecret}
$OAuth = Invoke-RestMethod -Method Post -Uri $LoginUrl/$TenantDomain/oauth2/token?api-version=1.0 -Body $RequestBody
$HeaderParams = @{'Authorization'="$($OAuth.Token_Type) $($Oauth.Access_Token)"}

#Retrieve current O365 health events posted for tenant
$O365Incidents = (Invoke-RestMethod -Method Get -Uri $Resource/api/v1.0/$TenantGUID/ServiceComms/Messages -Headers $HeaderParams).Value | Where {$_.MessageType -eq "Incident"}

#Get list of new or changed events
$NewChangedEvents = @()
ForEach ($Incident in $O365Incidents)
{
$NewChangedFlag = 0
If ($HistoryTable.ContainsKey($Incident.Id))
{
If ($HistoryTable[$Incident.Id] -ne (Get-Date($Incident.LastUpdatedTime)).ToLocalTime().ToString("yyyy/MM/dd HH:mm:ss")) {$NewChangedFlag = 1; $HistoryTable[$Incident.Id] = (Get-Date($Incident.LastUpdatedTime)).ToLocalTime().ToString("yyyy/MM/dd HH:mm:ss")}
}
Else
{
$HistoryTable.Add($Incident.Id,(Get-Date($Incident.LastUpdatedTime)).ToLocalTime().ToString("yyyy/MM/dd HH:mm:ss"))
$NewChangedFlag = 1
}

If ($NewChangedFlag -eq 1)
{
$LatestMessage = $($Incident.Messages | Sort-Object -Property PublishedTime)[$Incide3nt.Messages.Count - 1]
$Event = New-Object PSObject
$Event | Add-Member -Type NoteProperty -Name ID -Value $Incident.Id
$Event | Add-Member -Type NoteProperty -Name Service -Value $Incident.WorkloadDisplayName
$Event | Add-Member -Type NoteProperty -Name Status -Value $Incident.Status
$Event | Add-Member -Type NoteProperty -Name StartTime -Value (Get-Date($Incident.StartTime)).ToLocalTime().ToString("yyyy/MM/dd HH:mm:ss")
$Event | Add-Member -Type NoteProperty -Name LastUpdatedTime -Value (Get-Date($Incident.LastUpdatedTime)).ToLocalTime().ToString("yyyy/MM/dd HH:mm:ss")
$Event | Add-Member -Type NoteProperty -Name Details -Value $LatestMessage.MessageText
$Event | Add-Member -Type NoteProperty -Name NotificationRecipients $NotificationRecipients
$NewChangedEvents += @($Event)
}
}

ForEach ($Event in $NewChangedEvents)
{
#Build HTML for email
$MessageText = $Event.Details -replace("`n",'<br>') -replace([char]8217,"'") -replace([char]8220,'"') -replace([char]8221,'"') -replace('\[','<b><i>') -replace('\]','</i></b>')
$HTML = "<html>"
$HTML += "<style>"
$HTML += "BODY{font-family: Arial; font-size: 10pt;}"
$HTML += "H1{font-size: 22px;}"
$HTML += "H2{font-size: 18px; padding-top: 10px;}"
$HTML += "H3{font-size: 16px; padding-top: 8px;}"
$HTML += "H4{font-size: 12px; padding-top: 4px;}"
$HTML += "TABLE{border: 1px solid black; border-collapse: collapse; font-size: 8pt; table-layout: fixed; width: 800px;}"
$HTML += "TABLE.summary{text-align: center; width: auto;}"
$HTML += "TH{border: 1px solid black; background: #dddddd; padding: 5px; color: #000000;}"
$HTML += "TD{border: 1px solid black; padding: 5px; vertical-align: top; }"
$HTML += "td.pass{background: #7FFF00;}"
$HTML += "td.warn{background: #FFE600;}"
$HTML += "td.fail{background: #FF0000; color: #ffffff;}"
$HTML += "td.info{background: #85D4FF;}"
$HTML += "ul{list-style: inside; padding-left: 0px;}"
$HTML += ".firstrunnotice { font-size: 14px; color: #4286f4; }"
$HTML += "</style>"
$HTML += "<body>"
$HTML += "<table>"
$HTML += "<tr bgcolor=""#000099"">"
$HTML += " <td align=""center""><font color=""#ffffff"">Event ID</font></td>"
$HTML += " <td align=""center""><font color=""#ffffff"">Service</font></td>"
$HTML += " <td align=""center""><font color=""#ffffff"">Status</font></td>"
$HTML += " <td align=""center""><font color=""#ffffff"">Event Start Time</font></td>"
$HTML += " <td align=""center""><font color=""#ffffff"">Last Updated</font></td>"
$HTML += "</tr>"
$HTML += "<tr bgcolor=""#0000FF"">"
$HTML += " <td align=""center""><font color=""#ffffff"">$($Event.ID)</font></td>"
$HTML += " <td align=""center""><font color=""#ffffff"">$($Event.Service)</font></td>"
$HTML += " <td align=""center""><font color=""#ffffff"">$($Event.Status)</font></td>"
$HTML += " <td align=""center""><font color=""#ffffff"">$($Event.StartTime)</font></td>"
$HTML += " <td align=""center""><font color=""#ffffff"">$($Event.LastUpdatedTime)</font></td>"
$HTML += "<tr><td colspan=""5"" style=""border:none"">&nbsp;</td></tr>"
$HTML += "<tr>"
$HTML += " <td colspan=""5"">$MessageText<br/>&nbsp;<br/><a href=""http://o365health.ad.csbsju.edu/"">Office 365 Health Dashboard</a></td>"
$HTML += "</tr>"
$HTML += "<tr><td colspan=""5"" style=""border:none"">&nbsp;</td></tr>"
$HTML += "</table>"
$HTML += "</body>"
$HTML += "</html>"

#Send notification
Send-MailMessage -From $NotificationSender -To $NotificationRecipients -Subject "O365 Health Alert - $($Event.Service) [Event ID: $($Event.ID)]" -Body $HTML -BodyAsHtml -SmtpServer $SmtpServer -Port $SmtpPort -UseSsl
}