GCP OIDC proxy URL creation portion of handle_request

main.py

def handle_request(proxied_request):
    """Proxy the given request to the URL in the Forward-Host header with an
    Authorization header set using an OIDC bearer token for the Cloud
    Function's service account. If the header is not present, return a 400
    error.
    """

    host = proxied_request.headers.get(HOST_HEADER)
    if not host:
        return 'Required header {} not present'.format(HOST_HEADER), 400

    scheme = proxied_request.headers.get('X-Forwarded-Proto', 'https')
    url = '{}://{}{}'.format(scheme, host, proxied_request.path)
    headers = dict(proxied_request.headers)