Acessing Google Calendar API from Windows Service - vb.net

Question

I am writing a windows service application in Visual Studio (VB) that polls a users google calendar for any events that are happening within the next 5 minutes.
Ideally, I'd like my service to generate the credentials, but I don't think a windows service can pop up a browser page to authenticate someone. Currently I am generating the credentials in a specific location from a console app that can pop up a browser, and having the service look for credentials in that location. I'd like to get rid of the console app altogether, but if it's necessary I'll just run it in the batch file that installs the service.
The big issue I'm having is generating the credentials file (secondary concern), and more importantly refreshing it so it doesn't expire after an hour (primary concern).
Here is my windows service code (this works perfectly fine for the hour after I run my console app and allow access to my calendar):
Dim Scopes As String() = {CalendarService.Scope.CalendarReadonly}
Dim ApplicationName As String = "Google Calendar API .NET Quickstart"
Private Sub writeUpdateTimerEvent(source As Object, e As ElapsedEventArgs)
Dim credential As UserCredential
Try
Using stream = New FileStream("FILE PATH TO client_secret.json", FileMode.Open, FileAccess.Read)
Dim credPath As String = "FILE PATH TO WHERE MY CONSOLE APP IS STORING THE CREDENTIALS FILE"
credPath = Path.Combine(credPath, ".credentials/calendar-dotnet-quickstart.json")
credential = GoogleWebAuthorizationBroker.AuthorizeAsync(GoogleClientSecrets.Load(stream).Secrets, Scopes, "user", CancellationToken.None, New FileDataStore(credPath, True)).Result
If credential Is Nothing Then
credential.RefreshTokenAsync(CancellationToken.None)
End If
End Using
' Create Google Calendar API service.
Dim service = New CalendarService(New BaseClientService.Initializer() With {
.HttpClientInitializer = credential,
.ApplicationName = ApplicationName
})
' Define parameters of request.
Dim request As EventsResource.ListRequest = service.Events.List("primary")
request.TimeMin = DateTime.Now
request.TimeMax = DateTime.Now.AddMinutes(5)
request.ShowDeleted = False
request.SingleEvents = True
request.OrderBy = EventsResource.ListRequest.OrderByEnum.StartTime
' List events.
Dim eventsString As String = ""
Dim events As Events = request.Execute()
If events.Items IsNot Nothing AndAlso events.Items.Count > 0 Then
'This is where I do my operations on events occuring in the next 5 minutes
EventLog1.WriteEntry("Event occuring within 5 minutes")
Else
EventLog1.WriteEntry("No event occuring within 5 minutes")
End If
Catch ex As Exception
EventLog1.WriteEntry("error grabbing events." & Environment.NewLine & ex.message)
End Try
End Sub
Here is my console app code (pretty much the same as above):
Module Module1
Dim Scopes As String() = {CalendarService.Scope.CalendarReadonly}
Dim ApplicationName As String = "Google Calendar API .NET Quickstart"
Sub Main()
Dim credential As UserCredential
Using stream = New FileStream("client_secret.json", FileMode.Open, FileAccess.Read)
Dim credPath As String = "SAME FILE PATH AS IN MY SERVICE"
credPath = Path.Combine(credPath, ".credentials/calendar-dotnet-quickstart.json")
credential = GoogleWebAuthorizationBroker.AuthorizeAsync(GoogleClientSecrets.Load(stream).Secrets, Scopes, "user", CancellationToken.None, New FileDataStore(credPath, True)).Result
Console.WriteLine(Convert.ToString("Credential file saved to: ") & credPath)
End Using
' Create Google Calendar API service.
Dim service = New CalendarService(New BaseClientService.Initializer() With {
.HttpClientInitializer = credential,
.ApplicationName = ApplicationName
})
' Define parameters of request.
Dim request As EventsResource.ListRequest = service.Events.List("primary")
request.TimeMin = DateTime.Now
request.ShowDeleted = False
request.SingleEvents = True
request.MaxResults = 10
request.OrderBy = EventsResource.ListRequest.OrderByEnum.StartTime
' List events.
Dim events As Events = request.Execute()
Console.WriteLine("Upcoming events:")
If events.Items IsNot Nothing AndAlso events.Items.Count > 0 Then
For Each eventItem As Object In events.Items
Dim [when] As String = eventItem.Start.DateTime.ToString()
If [String].IsNullOrEmpty([when]) Then
[when] = eventItem.Start.[Date]
End If
Console.WriteLine("{0} ({1})", eventItem.Summary, [when])
Next
Console.WriteLine("You may now close this window.")
System.Environment.Exit(0)
Else
Console.WriteLine("No upcoming events found.")
End If
Console.Read()
End Sub
End Module

Answer 1

Got it working now, using a service account instead of a user account. No need for dealing with generating credentials or refreshing the token.
Dim serviceAccountEmail As [String] = ConfigurationManager.AppSettings("ServiceAcct")
Dim certificate = New X509Certificate2("key.p12", "notasecret", X509KeyStorageFlags.Exportable)
Dim credential1 As New ServiceAccountCredential(New ServiceAccountCredential.Initializer(serviceAccountEmail) With {
.Scopes = Scopes
}.FromCertificate(certificate))
Dim service = New CalendarService(New BaseClientService.Initializer() With {
.HttpClientInitializer = credential1,
.ApplicationName = ApplicationName
})