Adding facebook login to Flask-security - facebook-oauth

Question

I am having a trouble adding a "login with Facebook" feature to my Flask application which already using Flask-Security for the User authentication. What I really want is a Facebook button besides the login form, so that one can use Facebook instead of mail/password.
I have tried to do this with Facebook-social but failed, I don't really understand the docs. It seems to me that the user would have to be registered before connecting the account to Facebook, which is not the way I want it.
Is there anyone out there who have accomplished this? It seems to me that this would be a common case, but I can't find anything useful about it when googling.

Answer 1

I've done something similar, though with our own SSO instead of Facebook, but the principles are the same. In our case, we're using CAS, so #login_required redirects to our CAS login. On successful login, I use the CAS username attribute to dynamically add the user, then login via Flask-Security. Note that my example makes assumptions about your setup based on https://pythonhosted.org/Flask-Security/quickstart.html
def add_user(username):
if not user_datastore.find_user(username=username):
user_datastore.create_user(**get_user_data(username))
user_datastore.commit()
db.session.commit()
def get_user_data(username):
<Return dict mapping Facebook data to your user model>
def set_current_login(username):
try:
add_user(username)
security.current_user = user_datastore.find_user(username=username)
except Exception as e:
print str(e)
return False
return True
#app.route('/')
#login_required
def index():
set_current_login(<facebook username var>)
Note that you can also use the flask_security.utils.login_user() routine instead of setting the current_user object, which will also set a Flask-Security session cookie.
See the API documentation at https://pythonhosted.org/Flask-Security/api.html