auth.py

from __future__ import print_function
import pickle
import os.path
from google_auth_oauthlib.flow import InstalledAppFlow
from google.auth.transport.requests import Request

# If modifying these scopes, delete the file token.pickle.
SCOPES = ["https://mail.google.com/"]


def main():
    """Authorize the user by OAth 2.0"""
    creds = None
    # The file token.pickle 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.pickle"):
        with open("token.pickle", "rb") as token:
            creds = pickle.load(token)
    # 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:
            creds.refresh(Request())
        else:
            flow = InstalledAppFlow.from_client_secrets_file("credentials.json", SCOPES)
            creds = flow.run_local_server(port=1234)
        # Save the credentials for the next run
        with open("token.pickle", "wb") as token:
            pickle.dump(creds, token)


if __name__ == "__main__":
    main()