auth.py

import os
import os.path

from google.auth.exceptions import RefreshError
from google.auth.transport.requests import Request
from google.oauth2.credentials import Credentials
from google_auth_oauthlib.flow import InstalledAppFlow

import web_pdb


TOKEN_FILE = "token.json"
# If modifying these scopes, delete the TOKEN_FILE.
SCOPES = ["https://www.googleapis.com/auth/drive"]


def auth():
    creds = None
    # The file token.json stores the user's access and refresh tokens, and is
    # created automatically when the authorization flow completes for the first
    # time.
    if os.path.exists(TOKEN_FILE):
        creds = Credentials.from_authorized_user_file(TOKEN_FILE, SCOPES)
    # If there are no (valid) credentials available, let the user log in.
    if not creds or not creds.valid:
        if creds and creds.expired and creds.refresh_token:
            with web_pdb.catch_post_mortem():
                try:
                    creds.refresh(Request())
                except RefreshError:
                    os.unlink(TOKEN_FILE)
                    return auth()
        else:
            flow = InstalledAppFlow.from_client_secrets_file("credentials.json", SCOPES)
            creds = flow.run_local_server(port=0)
        # Save the credentials for the next run
        with open(TOKEN_FILE, "w") as token:
            token.write(creds.to_json())

    return creds