def authenticate():
callback = url_for("authenticate", _external=True)
code = request.args["code"]
access_token = Foursquare.get_access_token(
CLIENT_ID, CLIENT_SECRET,
callback, code
)
session["access_token"] = access_token
session["user"] = get_user()
session["is_login"] = True
return redirect(url_for("index"))
