B4X

OAuth2 for a GMail using a JSON Service Account Key

See more GMail SMTP/IMAP/POP Examples

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. B4X

Dim success As Boolean = False

'  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.
Dim fac As ChilkatFileAccess
fac.Initialize
Dim jsonKey As String = fac.ReadEntireTextFile("qa_data/googleApi/chilkat25-b4214220e565.json", "utf-8")
If fac.LastMethodSuccess <> True Then
    Log(fac.LastErrorText)
    Return
End If


'  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"
'  }

Dim gAuth As ChilkatAuthGoogle
gAuth.Initialize("gAuth")
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
Dim tlsSock As ChilkatSocket
tlsSock.Initialize("tlsSock")
success = tlsSock.Connect("www.googleapis.com", 443, True, 5000)
If success <> True Then
    Log(tlsSock.LastErrorText)
    Return
End If


'  Send the request to obtain the access token.
success = gAuth.ObtainAccessToken(tlsSock)
If success <> True Then
    Log(gAuth.LastErrorText)
    Return
End If


'  Examine the access token:
Dim accessToken As String = gAuth.AccessToken
Log("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.

'  -----------------------------------------------------------------------
Dim mailman As ChilkatMailMan
mailman.Initialize("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
Dim email As ChilkatEmail
email.Initialize

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 <> True Then
    Log(mailman.LastErrorText)
    Return
End If


success = mailman.CloseSmtpConnection
If success <> True Then
    Log("Connection to SMTP server not closed cleanly.")
End If


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