(Go) OAuth2 for a GMail using a P12 Service Account Key

See more GMail REST API Examples

Note: This example does not work for Personal Google Accounts where the email domain is @gmail.com

For more information, see https://www.chilkatsoft.com/google_workspace_setup_smtp_gmail.asp

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

    http := Http_Ref.html">chilkat.NewHttp()

    // --------------------------------------------------------------------------------
    // 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
    // --------------------------------------------------------------------------------
    // Begin by loading your Google service account key (.p12)
    cert := Cert_Ref.html">chilkat.NewCert()
    success := cert.LoadPfxFile("c:/someDirectory/keys/chilkat25-cbd7b42afbd8.p12","notasecret")
    if success != true {
        fmt.Println(cert.LastErrorText())
        http.DisposeHttp()
        cert.DisposeCert()
        return
    }

    // The ISS is your service account email address ending in gserviceaccount.com.
    iss := "chilkatsvc@chilkat25.iam.gserviceaccount.com"

    // The scope is always the following string:
    scope := "https://mail.google.com/"

    // The sub is your company email address
    oauth_sub := "bob@yourcompany.com"

    // The access token is valid for this number of seconds.
    numSec := 3600

    accessToken := http.G_SvcOauthAccessToken(iss,scope,oauth_sub,numSec,cert)
    if http.LastMethodSuccess() != true {
        fmt.Println(http.LastErrorText())
        http.DisposeHttp()
        cert.DisposeCert()
        return
    } else {
        fmt.Println("access token: ", *accessToken)
    }

    // 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 := MailMan_Ref.html">chilkat.NewMailMan()

    // Set the properties for the GMail SMTP server:
    mailman.SetSmtpHost("smtp.gmail.com")
    mailman.SetSmtpPort(587)
    mailman.SetStartTLS(true)

    mailman.SetSmtpUsername("bob@yourcompany.com")
    mailman.SetOAuth2AccessToken(*accessToken)

    // Create a new email object
    email := Email_Ref.html">chilkat.NewEmail()

    email.SetSubject("This is a test")
    email.SetBody("This is a test")
    email.SetFrom("Bob <bob@yourcompany.com>")
    success = email.AddTo("Recipient","recipient@example.com")
    // To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

    success = mailman.SendEmail(email)
    if success != true {
        fmt.Println(mailman.LastErrorText())
        http.DisposeHttp()
        cert.DisposeCert()
        mailman.DisposeMailMan()
        email.DisposeEmail()
        return
    }

    success = mailman.CloseSmtpConnection()
    if success != true {
        fmt.Println("Connection to SMTP server not closed cleanly.")
    }

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

    http.DisposeHttp()
    cert.DisposeCert()
    mailman.DisposeMailMan()
    email.DisposeEmail()