https://{SLUG}.nationbuilder.com/oauth/authorize?response_type=code&client_id={CLIENT_ID}&redirect_uri={REDIRECT}
curl -X POST --header "Content-Type: application/json" --header "Accept: application/json" --data '{"grant_type":"authorization_code", "client_id":"{CLIENT_ID}", "client_secret":"{CLIENT_SECRET}", "redirect_uri":"{REDIRECT}", "code":"{CODE}"}' https://{SLUG}.nationbuilder.com/oauth/token