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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 B4X

Dim success As Boolean = False

'  This example assumes 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
'  --------------------------------------------------------------------------------

Dim http As ChilkatHttp
http.Initialize("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:
Dim cert As ChilkatCert
cert.Initialize("cert")
success = cert.LoadPfxFile("/myDir/API Project-1c43a291e2a1-notasecret.p12", "notasecret")
If success <> True Then
    Log(cert.LastErrorText)
    Return
End If


'  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).

Dim claimParams As ChilkatHashtable
claimParams.Initialize

'  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.
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")

Dim numSec As Int = 3600

Dim accessToken As String = http.G_SvcOauthAccessToken2(claimParams, numSec, cert)
If http.LastMethodSuccess <> True Then
    Log(http.LastErrorText)
Else
    Log("access token: " & accessToken)
End If