InvalidConfigError: Invalid client secrets file while saving PyDrive credentials - python-3.x

Question

I use a Colaboratory Notebook and tried to automate the GoogleAuth process while using PyDrive librairy.
I tried the way dano proposed here: https://stackoverflow.com/a/24542604/10131744
Nevertheless, I get an error, linked to client secret.
Here is my code:
from pydrive.auth import GoogleAuth
from pydrive.drive import GoogleDrive
from google.colab import auth
from oauth2client.client import GoogleCredentials
auth.authenticate_user()
gauth = GoogleAuth()
#gauth.credentials = GoogleCredentials.get_application_default()
gauth.LoadCredentialsFile("mycreds.txt")
if gauth.credentials is None:
# Authenticate if they're not there
gauth.LocalWebserverAuth()
elif gauth.access_token_expired:
# Refresh them if expired
gauth.Refresh()
else:
# Initialize the saved creds
gauth.Authorize()
gauth.SaveCredentialsFile("mycreds.txt")
drive = GoogleDrive(gauth)
And here is the message I get:
/usr/local/lib/python3.6/dist-packages/oauth2client/_helpers.py:255: UserWarning: Cannot access mycreds.txt: No such file or directory
warnings.warn(_MISSING_FILE_MESSAGE.format(filename))
---------------------------------------------------------------------------
FileNotFoundError Traceback (most recent call last)
/usr/local/lib/python3.6/dist-packages/oauth2client/clientsecrets.py in _loadfile(filename)
120 try:
--> 121 with open(filename, 'r') as fp:
122 obj = json.load(fp)
FileNotFoundError: [Errno 2] No such file or directory: 'client_secrets.json'
During handling of the above exception, another exception occurred:
InvalidClientSecretsError Traceback (most recent call last)
/usr/local/lib/python3.6/dist-packages/pydrive/auth.py in LoadClientConfigFile(self, client_config_file)
385 try:
--> 386 client_type, client_info = clientsecrets.loadfile(client_config_file)
387 except clientsecrets.InvalidClientSecretsError as error:
/usr/local/lib/python3.6/dist-packages/oauth2client/clientsecrets.py in loadfile(filename, cache)
164 if not cache:
--> 165 return _loadfile(filename)
166
/usr/local/lib/python3.6/dist-packages/oauth2client/clientsecrets.py in _loadfile(filename)
124 raise InvalidClientSecretsError('Error opening file', exc.filename,
--> 125 exc.strerror, exc.errno)
126 return _validate_clientsecrets(obj)
InvalidClientSecretsError: ('Error opening file', 'client_secrets.json', 'No such file or directory', 2)
During handling of the above exception, another exception occurred:
InvalidConfigError Traceback (most recent call last)
<ipython-input-9-370983bd3c5e> in <module>()
13 if gauth.credentials is None:
14 # Authenticate if they're not there
---> 15 gauth.LocalWebserverAuth()
16 elif gauth.access_token_expired:
17 # Refresh them if expired
/usr/local/lib/python3.6/dist-packages/pydrive/auth.py in _decorated(self, *args, **kwargs)
111 self.LoadCredentials()
112 if self.flow is None:
--> 113 self.GetFlow()
114 if self.credentials is None:
115 code = decoratee(self, *args, **kwargs)
/usr/local/lib/python3.6/dist-packages/pydrive/auth.py in GetFlow(self)
441 if not all(config in self.client_config \
442 for config in self.CLIENT_CONFIGS_LIST):
--> 443 self.LoadClientConfig()
444 constructor_kwargs = {
445 'redirect_uri': self.client_config['redirect_uri'],
/usr/local/lib/python3.6/dist-packages/pydrive/auth.py in LoadClientConfig(self, backend)
364 raise InvalidConfigError('Please specify client config backend')
365 if backend == 'file':
--> 366 self.LoadClientConfigFile()
367 elif backend == 'settings':
368 self.LoadClientConfigSettings()
/usr/local/lib/python3.6/dist-packages/pydrive/auth.py in LoadClientConfigFile(self, client_config_file)
386 client_type, client_info = clientsecrets.loadfile(client_config_file)
387 except clientsecrets.InvalidClientSecretsError as error:
--> 388 raise InvalidConfigError('Invalid client secrets file %s' % error)
389 if not client_type in (clientsecrets.TYPE_WEB,
390 clientsecrets.TYPE_INSTALLED):
InvalidConfigError: Invalid client secrets file ('Error opening file', 'client_secrets.json', 'No such file or directory', 2)
I've tried to add a client_secrets.json file according to this answer: https://stackoverflow.com/a/33426759/10131744
But either I did something wrong, or the .json file is not in the right place, but it doesn't work.
Thanks a lot for your help.