Adding a Custom Backed to python-social-auth

I am trying to add a custom backend and here is the code. I had copied it from Google backend.

class BaseMyAuthAuth(object):
    def get_user_id(self, details, response):
        """Use google email as unique id"""
        if self.setting('USE_UNIQUE_USER_ID', False):
            if 'sub' in response:
                return response['sub']
            else:
                return response['id']
        else:
            return details['email']

    def get_user_details(self, response):
        """Return user details from Google API account"""
        if 'username' in response:
            email = response['username']
        else:
            email = ''

        name, given_name, family_name = (
            response.get('name', ''),
            response.get('given_name', ''),
            response.get('family_name', ''),
        )

        fullname, first_name, last_name = self.get_user_names(
            name, given_name, family_name
        )
        return {'username': email.split('@', 1)[0],
                'email': email,
                'fullname': fullname,
                'first_name': first_name,
                'last_name': last_name}

class BaseMyAuthOAuth2API(BaseMyAuthAuth):
    def user_data(self, access_token, *args, **kwargs):
        """Return user data from Google API"""
        url = urljoin(self.API_URL, '/oauth/me')
        return self.get_json(
            url,
            headers={
                'Authorization': 'Bearer %s' % access_token,
            },
        )

    def revoke_token_params(self, token, uid):
        return {'token': token}

    def revoke_token_headers(self, token, uid):
        return {'Content-type': 'application/json'}

class MyAuthOAuth2(BaseMyAuthOAuth2API, BaseOAuth2):
    """Google OAuth2 authentication backend"""
    name = 'myauth'
    REDIRECT_STATE = False
    API_URL = settings.AUTH_URL
    AUTHORIZATION_URL = settings.AUTH_AUTHORIZE_URL
    ACCESS_TOKEN_URL = settings.AUTH_ACCESS_TOKEN_URL
    ACCESS_TOKEN_METHOD = 'POST'
    # The order of the default scope is important
    #DEFAULT_SCOPE = ['openid', 'email', 'profile']
    EXTRA_DATA = [
        ('refresh_token', 'refresh_token', True),
        ('expires_in', 'expires'),
        ('token_type', 'token_type', True)
    ]

It runs well and fetches all the user data needed, but after that it always try to create a new user, on the other hand. If we see Google backend does not create a new user if the user already exists.

My custom backend gives me issue on this file at path

/venv/lib/python3.6/site-packages/django/contrib/auth/__init__.py

        try:
            user = backend.authenticate(request, **credentials)
        except PermissionDenied:
            # This backend says to stop in our tracks - this user should not be allowed in at all.
            break

and google backend goes to different path /venv/lib/python3.6/site-packages/rest_framework_social_oauth2/oauth2_grants.py

        try:
            user = backend.do_auth(access_token=request.token)
        except requests.HTTPError as e:
            raise errors.InvalidRequestError(
                description="Backend responded with HTTP{0}: {1}.".format(e.response.status_code,
                                                                          e.response.text),
                request=request)

this is the difference I have found out so far.

RealmTeam / django-rest-framework-social-oauth2

Adding a Custom Backed to python-social-auth #200