(Ruby) OAuth2 for a GMail using a JSON Service Account Key

Demonstrates how get an OAuth2 access token for GMail (Google Service Account) using a JSON private key.

After the access token is obtained, it may be used to send email. When the access token expires, a new access token needs to be obtained (using this same procedure).

Note: This is for OAuth2 using Google Service account keys.

Chilkat Ruby Downloads install from rubygems.org gem install chilkat or download... Ruby Library for Windows, MacOS, Linux, Alpine Linux

require 'chilkat'

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

# First load the JSON key into a string.
fac = Chilkat::CkFileAccess.new()
jsonKey = fac.readEntireTextFile("qa_data/googleApi/ChilkatTest-ab2ecd52ef98.json","utf-8")
if (fac.get_LastMethodSuccess() != true)
    print fac.lastErrorText() + "\n";
    exit
end

# A JSON private key should look like this:

# 	{
# 	  "type": "service_account",
# 	  "project_id": "chilkattest-1350",
# 	  "private_key_id": "fa2e36ee26986eab628b59868af8bec1d1c64c38",
# 	  "private_key": "-----BEGIN PRIVATE KEY-----\nMIIEvgIjFa...28N64N2n1E4FYzBZjSdy\n-----END PRIVATE KEY-----\n",
# 	  "client_email": "598922945226-00rb0ppfg0sndajo6bhvd4v17jtj2d3a@developer.gserviceaccount.com",
# 	  "client_id": "598922945226-00rb0ppfg0snd9jo7bhvd4v17jtj2d3a.apps.googleusercontent.com",
# 	  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
# 	  "token_uri": "https://accounts.google.com/o/oauth2/token",
# 	  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
# 	  "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/598922945226-00rb0ppfg0sndajo6bhvd4v17jtj2d3a%40developer.gserviceaccount.com"
# 	}

gAuth = Chilkat::CkAuthGoogle.new()
gAuth.put_JsonKey(jsonKey)

# Choose a scope.
gAuth.put_Scope("https://mail.google.com/")

# Request an access token that is valid for this many seconds.
gAuth.put_ExpireNumSeconds(3600)

# If the application is requesting delegated access:
# The email address of the user for which the application is requesting delegated access,
# then set the email address here. (Otherwise leave it empty.)
gAuth.put_SubEmailAddress("")

# Connect to www.googleapis.com using TLS (TLS 1.2 is the default.)
# The Chilkat socket object is used so that the connection can be established
# through proxies or an SSH tunnel if desired.
tlsSock = Chilkat::CkSocket.new()
success = tlsSock.Connect("www.googleapis.com",443,true,5000)
if (success != true)
    print tlsSock.lastErrorText() + "\n";
    exit
end

# Send the request to obtain the access token.
success = gAuth.ObtainAccessToken(tlsSock)
if (success != true)
    print gAuth.lastErrorText() + "\n";
    exit
end

# Examine the access token:
print "Access Token: " + gAuth.accessToken() + "\n";

# Now that we have the access token, it may be used to send email
# while it remains valid.  Once the access token expires, a new access token 
# should be obtained using the same code as above.

# -----------------------------------------------------------------------
mailman = Chilkat::CkMailMan.new()

# Set the properties for the GMail SMTP server:
mailman.put_SmtpHost("smtp.gmail.com")
mailman.put_SmtpPort(587)
mailman.put_StartTLS(true)

mailman.put_SmtpUsername("YOUR_GOOGLE_APPS_USER_EMAIL_ADDRESS")
mailman.put_OAuth2AccessToken(gAuth.accessToken())

# Create a new email object
email = Chilkat::CkEmail.new()

email.put_Subject("This is a test")
email.put_Body("This is a test")
email.put_From("YOUR NAME <YOUR_GOOGLE_APPS_USER_EMAIL_ADDRESS>")
success = email.AddTo("Chilkat Admin","admin@chilkatsoft.com")
# To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

# Call SendEmail to connect to the SMTP server and send.
# The connection (i.e. session) to the SMTP server remains
# open so that subsequent SendEmail calls may use the
# same connection.  
success = mailman.SendEmail(email)
if (success != true)
    print mailman.lastErrorText() + "\n";
    exit
end

# You may close the connection here.  If the connection is kept open, 
# the next call to mailman.SendEmail will continue using the already-established connection
# (and automatically re-connect if needed).
success = mailman.CloseSmtpConnection()
if (success != true)
    print "Connection to SMTP server not closed cleanly." + "\n";
end

print "Email Sent via GMail using an OAuth2 Service Account Key." + "\n";