Get long-lived Facebook token on connect or login

[dadoeyad]

This is an improvement request/suggestion more than an issue.
django-allauth allows exchanging the short-lived Facebook access token for a long-lived one by setting "EXCHANGE_TOKEN": True in the Facebook provider settings.

Code in django-allauth:

https://github.com/pennersr/django-allauth/blob/25fe632acf12571ae2ac9e692e8890019d5a6e7b/allauth/socialaccount/providers/facebook/views.py#L97-L108

I needed django-rest-auth to do the same and did it by overriding the get_social_login method in my FacebookSocialConnectSerializer

def get_social_login(self, *args, **kwargs):
        social_login = super(FacebookSocialConnectSerializer, self).get_social_login(*args, **kwargs)
        # Get long-lived token
        request = self._get_request()

        provider = providers.registry.by_id(
            FacebookProvider.id, request
        )
        app = provider.get_app(request)

        resp = requests.get(
            GRAPH_API_URL + '/oauth/access_token',
            params={'grant_type': 'fb_exchange_token',
                    'client_id': app.client_id,
                    'client_secret': app.secret,
                    'fb_exchange_token': social_login.token}).json()
        access_token = resp['access_token']
        expires_at = None
        expires_in = resp.get('expires_in')
        if expires_in:
            expires_at = timezone.now() + timedelta(
                seconds=int(expires_in))

        token = SocialToken(app=app,
                            token=access_token,
                            expires_at=expires_at)
        social_login.token = token
        return social_login

If you think django-rest-auth would benefit from this, I'll be happy to open a pull request :)