(PowerShell) 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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Add-Type -Path "C:\chilkat\ChilkatDotNet47-x64\ChilkatDotNet47.dll"

# 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.
$fac = New-Object Chilkat.FileAccess
$jsonKey = $fac.ReadEntireTextFile("qa_data/googleApi/chilkat25-b4214220e565.json","utf-8")
if ($fac.LastMethodSuccess -ne $true) {
    $($fac.LastErrorText)
    exit
}

# 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"
# }

$gAuth = New-Object 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
$tlsSock = New-Object Chilkat.Socket
$success = $tlsSock.Connect("www.googleapis.com",443,$true,5000)
if ($success -ne $true) {
    $($tlsSock.LastErrorText)
    exit
}

# Send the request to obtain the access token.
$success = $gAuth.ObtainAccessToken($tlsSock)
if ($success -ne $true) {
    $($gAuth.LastErrorText)
    exit
}

# Examine the access token:
$accessToken = $gAuth.AccessToken
$("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.

# -----------------------------------------------------------------------
$mailman = New-Object Chilkat.MailMan

# Set the properties for the GMail SMTP server:
$mailman.SmtpHost = "smtp.gmail.com"
$mailman.SmtpPort = 587
$mailman.StartTLS = $true

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

# Create a new email object
$email = New-Object 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 -ne $true) {
    $($mailman.LastErrorText)
    exit
}

$success = $mailman.CloseSmtpConnection()
if ($success -ne $true) {
    $("Connection to SMTP server not closed cleanly.")
}

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