Python | Technical Handbook

Flask - oauthlib.oauth2.rfc6749.errors.MismatchingStateError: (mismatching_state) CSRF Warning! State not equal in request and response.

Solution
Use 'Flow' instead of' 'InstalledAppFlow' from 'from google_auth_oauthlib.flow'

By using the 'web' key in the CLIENT_CONFIG dictionary, you indicate that you're configuring the OAuth flow for a web application