Creating a v4 signed url

General
1

Does any one have any idea how to generate a v4 signed url without resorting to a keyfile?
when using ADC from my firebase workstation and calling:

      signed_url = blob.generate_signed_url(
           version="v4",
           expiration=timedelta(minutes=15),
           method="GET",
           service_account_email=target_service_account_email,  
           access_token=None 
      )

I get this error:
you need a private key to sign credentials.the credentials you are currently using <class ‘google.auth.compute_engine.credentials.Credentials’> just contains a token. see Authentication — google-api-core documentation for more details.