The client uses the private mobile Google Keep API. Authentication requires a master token for the account, which provides full access. Protect this token like a password.
Use Keep.authenticate(username, master_token) to log in. It is recommended to store the token in a platform secrets store (like keyring) rather than hardcoding it in your script.
import keyring
import gkeepapi
# To save the token
# keyring.set_password('google-keep-token', 'user@gmail.com', master_token)
master_token = keyring.get_password("google-keep-token", "user@gmail.com")
keep = gkeepapi.Keep()
keep.authenticate('user@gmail.com', master_token)