Fitbit to SparkyFitness connection illustration
The Setup
I had SparkyFitness running in my homelab at https://address.yourdomain.com, proxyed through Nginx Proxy Manager. Everything worked fine — until I tried to connect my Fitbit account.
The Problem
I registered a Fitbit developer app, entered the Client ID and Client Secret into SparkyFitness, clicked Connect to Fitbit, and immediately hit a wall:
403 Forbidden
The authorization URL looked like this:
https://www.fitbit.com/oauth2/authorize?…&redirect_uri=http://192.168.1.101:80/fitbit/callback&…
Fitbit was trying to redirect back to my local LAN IP — http://192.168.1.101:80 — which is obviously not reachable from the outside world. The callback never made it back to my server.
The Fix
The issue was a single environment variable on my SparkyFitness server:
SPARKY_FITNESS_FRONTEND_URL=http://192.168.1.101:80
This was set to the local IP of my SparkyFitness LXC. SparkyFitness uses this variable to build all its public-facing URLs — including the OAuth redirect URI sent to Fitbit. With it pointing to a LAN address, Fitbit’s callback had nowhere to go.
I updated the .env file:
SPARKY_FITNESS_FRONTEND_URL=https://address.yourdomain.com
Then restarted the services:
systemctl restart sparkyfitness-server nginx
Clicked Connect to Fitbit again — this time the redirect URI in the authorization URL pointed to https://address.yourdomain.com/fitbit/callback. Fitbit authenticated, redirected back, and SparkyFitness successfully synced my Fitbit data.
The Lesson
If you’re self-hosting SparkyFitness (or any app with OAuth) behind a reverse proxy, and OAuth logins are failing with a 403 — check your SPARKY_FITNESS_FRONTEND_URL first. It’s likely pointing to an internal address that external services can’t reach.
All external callbacks need to go through your public domain, not your LAN IP.
TL;DR
- Locate your SPARKY_FITNESS_FRONTEND_URL in /etc/sparkyfitness/.env
- Change it from http://192.168.1.101:80: to https://address.yourdomain.com
- Run systemctl restart sparkyfitness-server nginx
- Try connecting Fitbit again
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