(google.oauth2) Error creating a Credential object: AttributeError: 'str' object has no attribute 'keys'

Question

I'm trying to create a Credential object using the classmethod from_authorized_user_file(). I want to use a code and refresh token stored into a file. This is part of my code:

from google.oauth2.credentials import Credentials as cred
new_cred = cred.from_authorized_user_file('data.json')

The data inside data.json is:

{"token": "1111", "refresh_token": "2222", 
"token_uri": "https://oauth2.googleapis.com/token", 
"client_id": "3333.apps.googleusercontent.com", 
"client_secret": "4444", 
"scopes": ["https://www.googleapis.com/auth/youtube.readonly", "https://www.googleapis.com/auth/youtube.force-ssl"]}

And that is the error I got:

/srv/conda/envs/notebook/lib/python3.7/site-packages/six.py in iterkeys(d, **kw)
    579 if PY3:
    580     def iterkeys(d, **kw):
--> 581         return iter(d.keys(**kw))
    582 
    583     def itervalues(d, **kw):

AttributeError: 'str' object has no attribute 'keys'

I don't know why this is happening, it seems to treat the object as string rather than a json object. Anyone has some clue about this?