(Visual FoxPro) 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 ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loHttp
LOCAL loCert
LOCAL lnSuccess
LOCAL loClaimParams
LOCAL lnNumSec
LOCAL lcAccessToken

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

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Http')
loHttp = CreateObject('Chilkat.Http')

* 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:
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Cert')
loCert = CreateObject('Chilkat.Cert')
lnSuccess = loCert.LoadPfxFile("/myDir/API Project-1c43a291e2a1-notasecret.p12","notasecret")
IF (lnSuccess <> 1) THEN
    ? loCert.LastErrorText
    RELEASE loHttp
    RELEASE loCert
    CANCEL
ENDIF

* 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).

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Hashtable')
loClaimParams = CreateObject('Chilkat.Hashtable')

* The required claim parameters that must be provided by the application are
* the "iss" and "scope" params:
lnSuccess = loClaimParams.AddStr("iss","761326798069-r5mljlln1rd4lrbhg75efgigp36m78j5@developer.gserviceaccount.com")
lnSuccess = loClaimParams.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.
lnSuccess = loClaimParams.AddStr("sub","user@your-domain.com")

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

lnNumSec = 3600

lcAccessToken = loHttp.G_SvcOauthAccessToken2(loClaimParams,lnNumSec,loCert)
IF (loHttp.LastMethodSuccess <> 1) THEN
    ? loHttp.LastErrorText
ELSE
    ? "access token: " + lcAccessToken
ENDIF

RELEASE loHttp
RELEASE loCert
RELEASE loClaimParams