feat: Added Temporary token based authentication similar to cli --access-token-file

[AmitChotaliya]

Fixes #1165

This features allows using access token in the sdk without having any of the GCP related credentials.

Example Usage:

• Generate the token using CLI gcloud auth print-access-token --impersonate-service-account=abc@xyz.iam.gserviceaccount.com
• Generate the token using python.

from google.auth import compute_engine
from google.auth import default, credentials
from google.auth.transport.requests import Request
import google.auth
from google.cloud import compute_v1

def generate_access_token():    
    creds, project = google.auth.default()    
    
    creds.refresh(Request())
    return creds.token, creds.expiry

• Copy this access token to a different/local machine or container having no other google credentials.
• Set the required environment variable.

export GOOGLE_TEMPORARY_ACCESS_TOKEN=token copied from above

• Try running the following python code to verify if the credentials are working.

def list_virtual_machines(project_id, creds):
    # Create a client for Compute Engine with the provided access token
    compute_client = compute_v1.NetworksClient(credentials=creds)

    # List VMs
    vm_list = compute_client.list(project=project_id)

    # Print VM names
    print("Virtual Machines:")
    for vm in vm_list:
        print(vm.name)
os.environ["GOOGLE_TEMPORARY_ACCESS_TOKEN"] = "access token copied from above"
    creds, project_id = google.auth.default()    
    list_virtual_machines("bamboo-weft-375813", creds=creds)

It should work fine till the token is valid.

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