(PowerShell) Refresh GMail SMTP OAuth2 Access Token

Demonstrates how to refresh an access token for sending email via GMail (SMTP).

Chilkat .NET Downloads Chilkat .NET Assemblies Chilkat for Mono

Add-Type -Path "C:\chilkat\ChilkatDotNet47-9.5.0-x64\ChilkatDotNet47.dll"

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

# See Get GMail SMTP Access Token 
# for sample code showing how to obtain a GMail SMTP access token for desktop apps.

# It is assumed we previously obtained an OAuth2 access token for GMail (one with a scope for sending email).

$jsonToken = New-Object Chilkat.JsonObject
$success = $jsonToken.LoadFile("qa_data/tokens/_gmailSmtp.json")
if ($success -ne $true) {
    $("Failed to load _gmailSmtp.json")
    exit
}

# The access token JSON looks something like this:

# 	{ 
# 	 "access_token": "abac.Ci-ZabcdF37-NUrmSzxbHxTsMbtlN-uPfabcdAQN_2ekzj0s5ofCzRabcdTDMGaa2Q",
# 	 "token_type": "Bearer",
# 	 "expires_in": 3600,
# 	 "refresh_token": "1/lEe5abcdNJ77eOSDBabcdkQGVmDalkwabcdR2Hatbo"
# 	}
# 

$oauth2 = New-Object Chilkat.OAuth2

$oauth2.TokenEndpoint = "https://www.googleapis.com/oauth2/v4/token"

# Replace these with actual values.
$oauth2.ClientId = "GOOGLE-CLIENT-ID"
$oauth2.ClientSecret = "GOOGLE-CLIENT-SECRET"

# Get the "refresh_token"
$oauth2.RefreshToken = $jsonToken.StringOf("refresh_token")

# Send the HTTP POST to refresh the access token..
$success = $oauth2.RefreshAccessToken()
if ($success -ne $true) {
    $($oauth2.LastErrorText)
    exit
}

# The response contains a new access token, but we must keep
# our existing refresh token for when we need to refresh again in the future.
$jsonToken.UpdateString("access_token",$oauth2.AccessToken)

# Save the new JSON access token response to a file.
$sbJson = New-Object Chilkat.StringBuilder
$jsonToken.EmitCompact = $false
$jsonToken.EmitSb($sbJson)
$sbJson.WriteFile("qa_data/tokens/_gmailSmtp.json","utf-8",$false)

$("OAuth2 authorization granted!")
$("New Access Token = " + $oauth2.AccessToken)