Using an alternative system for login sends Slack invites to non hc auth users

As [instructed ](https://hackclub.slack.com/archives/C09D1E22CF5/p1773133928021449)by @24c02, I am opening an issue on this topic.

Steps to reproduce:

1. Go to https://canvas.awdevsoftware.org/login/canvas
2. DM me on slack (awdev) an non slack email and I'll add it to the system
3. Log into the Canvas LMS instance with the email
4. You *should* receive an email from Slack with the following:

I have verified this with 2 people that are not in the Slack. This app is not exclusively a HC app. It is a test instance that I have setup for evaluation purposes. This seems to happen to any app that uses OIDC.