(Ruby) Get OAuth 2.0 Access Token using G_SvcOauthAccessToken2

Obtains an OAUTH2 access token from the Google OAuth 2.0 Authorization Server using the G_SvcOauthAccessToken2 method. This is for Server to server applications using Google API's that need an access token. See https://developers.google.com/accounts/docs/OAuth2ServiceAccount

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

require 'chilkat'

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

http = Chilkat::CkHttp.new()

# When a service account (Client ID) is created at https://code.google.com/apis/console/
# Google will generate a P12 key.  This is a PKCS12 (PFX) file that you will download
# and save.  The password to access the contents of this file is "notasecret".
# NOTE: The Chilkat Pfx API provides the ability to load a PFX/P12 and re-save
# with a different password.

# Begin by loading the downloaded .p12 into a Chilkat certificate object:
cert = Chilkat::CkCert.new()
success = cert.LoadPfxFile("/myDir/API Project-1c43a291e2a1-notasecret.p12","notasecret")
if (success != true)
    print cert.lastErrorText() + "\n";
    exit
end

# The next (and final) step is to request the access token.  Chilkat internally
# does all the work of forming the JWT header and JWT claim set, encoding and
# signing the JWT, and sending the access token request.
# The application need only provide the inputs: The iss, scope(s), sub, and the
# desired duration with a max of 3600 seconds (1 hour).
# 
# Each of these inputs is defined as follows 
# (see https://developers.google.com/accounts/docs/OAuth2ServiceAccount
# iss: The email address of the service account.
# scope: A space-delimited list of the permissions that the application requests.
# sub: The email address of the user for which the application is requesting delegated access.
# numSec: The number of seconds for which the access token will be valid (max 3600).

claimParams = Chilkat::CkHashtable.new()

# The required claim parameters that must be provided by the application are
# the "iss" and "scope" params:
success = claimParams.AddStr("iss","761326798069-r5mljlln1rd4lrbhg75efgigp36m78j5@developer.gserviceaccount.com")
success = claimParams.AddStr("scope","https://mail.google.com/")

# The "sub" param is required if there is an email address, such as for a
# Google Apps domain—if you use Google Apps for Work, where the administrator of the Google Apps domain 
# can authorize an application to access user data on behalf of users in the Google Apps domain.
# 
# Comment out this line if there is no such email address.
# The typical case is that there is no such email address.
success = claimParams.AddStr("sub","user@your-domain.com")

# The "aud" parameter is optional.  If not set, it defaults to the value shown here:
success = claimParams.AddStr("aud","https://accounts.google.com/o/oauth2/token")

numSec = 3600

accessToken = http.g_SvcOauthAccessToken2(claimParams,numSec,cert)
if (http.get_LastMethodSuccess() != true)
    print http.lastErrorText() + "\n";
else
    print "access token: " + accessToken + "\n";
end