(Lianja) 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.

Chilkat Lianja Extension Download Chilkat Lianja Extension

// 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.
loFac = createobject("CkFileAccess")
lcJsonKey = loFac.ReadEntireTextFile("qa_data/googleApi/chilkat25-b4214220e565.json","utf-8")
if (loFac.LastMethodSuccess <> .T.) then
    ? loFac.LastErrorText
    release loFac
    return
endif

// 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"
// }

loGAuth = createobject("CkAuthGoogle")
loGAuth.JsonKey = lcJsonKey

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

// Request an access token that is valid for this many seconds.
loGAuth.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.
loGAuth.SubEmailAddress = "info@chilkat.xyz"

// Connect to www.googleapis.com using TLS
loTlsSock = createobject("CkSocket")
llSuccess = loTlsSock.Connect("www.googleapis.com",443,.T.,5000)
if (llSuccess <> .T.) then
    ? loTlsSock.LastErrorText
    release loFac
    release loGAuth
    release loTlsSock
    return
endif

// Send the request to obtain the access token.
llSuccess = loGAuth.ObtainAccessToken(loTlsSock)
if (llSuccess <> .T.) then
    ? loGAuth.LastErrorText
    release loFac
    release loGAuth
    release loTlsSock
    return
endif

// Examine the access token:
lcAccessToken = loGAuth.AccessToken
? "Access Token: " + lcAccessToken

// 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.

// -----------------------------------------------------------------------
loMailman = createobject("CkMailMan")

// Set the properties for the GMail SMTP server:
loMailman.SmtpHost = "smtp.gmail.com"
loMailman.SmtpPort = 587
loMailman.StartTLS = .T.

loMailman.SmtpUsername = "info@chilkat.xyz"
loMailman.OAuth2AccessToken = lcAccessToken

// Create a new email object
loEmail = createobject("CkEmail")

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

llSuccess = loMailman.SendEmail(loEmail)
if (llSuccess <> .T.) then
    ? loMailman.LastErrorText
    release loFac
    release loGAuth
    release loTlsSock
    release loMailman
    release loEmail
    return
endif

llSuccess = loMailman.CloseSmtpConnection()
if (llSuccess <> .T.) then
    ? "Connection to SMTP server not closed cleanly."
endif

? "Successfully sent email using Gmail with a service account key."


release loFac
release loGAuth
release loTlsSock
release loMailman
release loEmail