Outlook OAuth Callback Fails in n8n Docker Setup Due to localhost Redirect

It looks like your issue isn’t with the Outlook credential settings per se but with the OAuth2 callback URL being set to localhost. When you run n8n via Docker (especially on a Raspberry Pi behind Casa OS), the OAuth2 flow must use a callback URL that’s accessible by Microsoft’s servers—not localhost.

Below are some steps you can follow to resolve the issue:

1. Update the webhook URL

By default, n8n may be configured to use localhost for its callback URL. In a Docker setup you’ll need to expose an externally accessible URL. You can do this by setting the WEBHOOK_TUNNEL_URL environment variable (or using a reverse proxy with a public hostname) so that the callback URL is something like https://your-domain.com or your server’s IP address instead of localhost.

Example if using an environment variable:

YAMLCopied
environment:
  - WEBHOOK_TUNNEL_URL=https://your-domain.com

2. Update your Microsoft application registration

After changing the callback URL in n8n, update your OAuth2 app’s redirect URI in the Microsoft Application Registration Portal to match this publicly-accessible URL (e.g. https://your-domain.com/rest/oauth2-credential/callback). This ensures that when Microsoft redirects back, n8n can receive it.

3. Verify Docker port configuration

Make sure the Docker container’s ports (eg. 5678 or the port you have configured for n8n) are mapped correctly so that external requests can reach your instance.

4. Reattempt the connection

With the correct external callback URL configured on both n8n and in your Microsoft app registration, click “Connect my account” again to complete the OAuth2 flow. The Microsoft login window should now redirect properly instead of trying to connect to localhost.

These steps should help resolve the ERR_CONNECTION_REFUSED issue you’re encountering by ensuring Microsoft can properly reach the n8n server. If you continue to have issues, double-check your reverse proxy or DNS settings along with any firewall rules that might block the connection.

Below is some guidance to resolve the issue when connecting your Outlook credential in n8n running via Docker:

Use a Reachable Redirect URL

When n8n is running in a container, the OAuth callback URL (by default something like
http://localhost:5678/rest/oauth2-credential/callback) may not be accessible from your external browser. Instead of using “localhost”, use an address that’s reachable from your browser. For example, you might:

• Configure your Docker setup to expose the correct host IP or domain.
• Update your Microsoft Application Registration (in the Azure portal) so that the redirect URI matches the externally accessible URL (e.g. http://:5678/rest/oauth2-credential/callback).

Update the Registered App Settings

In the Azure app registration for Outlook credentials:

1. Copy the callback URL provided by n8n.
2. Replace “localhost” in the URL with the IP address or domain name that correctly points to your n8n instance.
3. Save the updated redirect URI in the Azure app settings.

Docker Considerations

In your Docker configuration (running on your RPI-Docker via Casa OS):

• Verify that you are mapping the host’s required port (in your case, port 5678) correctly.
• If your host uses a different internal/external networking address, adjust your Docker run command or environment variables accordingly.

Once these changes are made, try clicking “Connect my account” again. The OAuth window should now redirect to a reachable address, allowing the connection to complete successfully.

Additional Check Points

• Firewall/Proxy: Ensure that your Casa OS or network setup isn’t blocking the connection to the updated host address.
• Credential Configuration: Confirm that the settings in your Outlook credential (as documented in the Outlook credentials docs) match your setup and your Microsoft app registration.

By ensuring the redirect (callback) URL is accessible from your browser outside the Docker container, you should be able to complete the Outlook credential connection using Exchange Online.