(VBScript) OAuth2 for a GMail using a JSON Service Account Key

This example shows how to obtain an OAuth2 access token for Gmail using a Google Service Account and a JSON private key. Once acquired, the access token can be used to send emails. Remember, upon token expiration, this process needs to be repeated to obtain a new token. Note: This procedure is specific to OAuth2 with Google Service Account keys.

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Dim fso, outFile
Set fso = CreateObject("Scripting.FileSystemObject")
'Create a Unicode (utf-16) output text file.
Set outFile = fso.CreateTextFile("output.txt", True, True)

' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

' --------------------------------------------------------------------------------
' For a step-by-step guide for setting up your Google Workspace service account,
' see Setup Google Workspace Account for Sending SMTP GMail from a Service Account
' --------------------------------------------------------------------------------

' First load the JSON key into a string.
set fac = CreateObject("Chilkat.FileAccess")
jsonKey = fac.ReadEntireTextFile("qa_data/googleApi/chilkat25-b4214220e565.json","utf-8")
If (fac.LastMethodSuccess <> 1) Then
    outFile.WriteLine(fac.LastErrorText)
    WScript.Quit
End If

' A Google service account JSON private key looks like this:

' {
'   "type": "service_account",
'   "project_id": "chilkat25",
'   "private_key_id": "b4214220f565881e19eeb97c2699bf5a0d1e3e0b",
'   "private_key": "-----BEGIN PRIVATE KEY-----\nMIIEvQ...NXcM=\n-----END PRIVATE KEY-----\n",
'   "client_email": "chilkatsvc@chilkat25.iam.gserviceaccount.com",
'   "client_id": "109122032928932715958",
'   "auth_uri": "https://accounts.google.com/o/oauth2/auth",
'   "token_uri": "https://oauth2.googleapis.com/token",
'   "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
'   "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/chilkatsvc%40chilkat25.iam.gserviceaccount.com",
'   "universe_domain": "googleapis.com"
' }

set gAuth = CreateObject("Chilkat.AuthGoogle")
gAuth.JsonKey = jsonKey

' Specify a scope.
gAuth.Scope = "https://mail.google.com/"

' Request an access token that is valid for this many seconds.
gAuth.ExpireNumSeconds = 3600

' When using a Google Workspace account with Gmail APIs, a service account can impersonate a user 
' via a process called domain-wide delegation � and the "sub" claim in the JWT is what enables this.
' Domain-wide delegation allows a Google Workspace administrator to authorize a service account to 
' act on behalf of any user in the domain, without user interaction.

' This is required for server-to-server access to user data � such as reading/sending Gmail from a background service.
' This is your company email address.
gAuth.SubEmailAddress = "info@chilkat.xyz"

' Connect to www.googleapis.com using TLS
set tlsSock = CreateObject("Chilkat.Socket")
success = tlsSock.Connect("www.googleapis.com",443,1,5000)
If (success <> 1) Then
    outFile.WriteLine(tlsSock.LastErrorText)
    WScript.Quit
End If

' Send the request to obtain the access token.
success = gAuth.ObtainAccessToken(tlsSock)
If (success <> 1) Then
    outFile.WriteLine(gAuth.LastErrorText)
    WScript.Quit
End If

' Examine the access token:
accessToken = gAuth.AccessToken
outFile.WriteLine("Access Token: " & accessToken)

' Sample output:
' ya29.a0AW4XtxjGTD67Z8 .... IRw0218

' The access token allows us to send unlimited emails while it's valid. Once it expires, we must obtain and use a new one.

' -----------------------------------------------------------------------
set mailman = CreateObject("Chilkat.MailMan")

' Set the properties for the GMail SMTP server:
mailman.SmtpHost = "smtp.gmail.com"
mailman.SmtpPort = 587
mailman.StartTLS = 1

mailman.SmtpUsername = "info@chilkat.xyz"
mailman.OAuth2AccessToken = accessToken

' Create a new email object
set email = CreateObject("Chilkat.Email")

email.Subject = "This is a test"
email.Body = "This is a test"
email.From = "Chilkat Test <info@chilkat.xyz>"
success = email.AddTo("Chilkat Software","info@chilkatsoft.com")
' To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

success = mailman.SendEmail(email)
If (success <> 1) Then
    outFile.WriteLine(mailman.LastErrorText)
    WScript.Quit
End If

success = mailman.CloseSmtpConnection()
If (success <> 1) Then
    outFile.WriteLine("Connection to SMTP server not closed cleanly.")
End If

outFile.WriteLine("Successfully sent email using Gmail with a service account key.")

outFile.Close