Lua

Get Google API Access Token using JSON Private Key

See more Google APIs Examples

Demonstrates how to get a Google API access token using a JSON service account private key. Lua

local chilkat = require("chilkat")

-- 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.
local fac = chilkat.FileAccess.new()
local jsonKey = fac:read_entire_text_file("qa_data/googleApi/chilkat25-b4214220e565.json", "utf-8")
if not fac.last_method_success then
    print(fac.last_error_text)
    return
end

-- 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"
-- }

local gAuth = chilkat.AuthGoogle.new()
gAuth.json_key = jsonKey

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

-- Request an access token that is valid for this many seconds.
gAuth.expire_num_seconds = 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.sub_email_address = "info@chilkat.xyz"

-- Connect to www.googleapis.com using TLS
local tlsSock = chilkat.Socket.new()
local success = tlsSock:connect("www.googleapis.com", 443, true, 5000)
if not success then
    print(tlsSock.last_error_text)
    return
end

-- Send the request to obtain the access token.
success = gAuth:obtain_access_token(tlsSock)
if not success then
    print(gAuth.last_error_text)
    return
end

-- Examine the access token:
local accessToken = gAuth.access_token
print("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.

-- -----------------------------------------------------------------------
local mailman = chilkat.MailMan.new()

-- Set the properties for the GMail SMTP server:
mailman.smtp_host = "smtp.gmail.com"
mailman.smtp_port = 587
mailman.start_tls = true

mailman.smtp_username = "info@chilkat.xyz"
mailman.oauth2_access_token = accessToken

-- Create a new email object
local email = chilkat.Email.new()

email.subject = "This is a test"
email.body = "This is a test"
email.from = "Chilkat Test <info@chilkat.xyz>"
success = email:add_to("Chilkat Software", "info@chilkatsoft.com")
-- To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

success = mailman:send_email(email)
if not success then
    print(mailman.last_error_text)
    return
end

success = mailman:close_smtp_connection()
if not success then
    print("Connection to SMTP server not closed cleanly.")
end

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