(VB.NET) 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

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

Dim http As New 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:
Dim cert As New Chilkat.Cert
Dim success As Boolean = cert.LoadPfxFile("/myDir/API Project-1c43a291e2a1-notasecret.p12","notasecret")
If (success <> True) Then
    Debug.WriteLine(cert.LastErrorText)
    Exit Sub
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 New Chilkat.Hashtable

' 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")

Dim numSec As Integer = 3600

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