Backend: Improve error screen from /auth/callback endpoint

[19mdavenport]

Currently when something goes wrong with the CAS auth callback the user gets an annoying screen with an unhelpful error message. I would think this could be improved if a TA is interested. Not sure how you would test that but one way this happens is if someone not currently taking, instructing, or TAing for 240 tries to login, they get an unhelpful message . I suspect this may be inside a method inside CanvasIntegrationImpl which may always assume a response with an array length of one, which wouldn't be the case for someone not in the current canvas course.

This can also happen if the CAS redirect takes too long .

[mewilker]

@19mdavenport I'm reworking the authentication and there is some sensitve information I need to ask you about. Send me an email at mewilk561@gmail.com if you can please.

[TheDavSmasher]

@19mdavenport I'm more curious where this message is handled to be printed to the screen, as I'm unsure where this callback is handled where we would add something

[19mdavenport]

@TheDavSmasher These both happen when a runtime exception (In both of these cases, a NullPointerException is thrown by something the autograder code is doing and caught by Javalin code rather than autograder code. The first is in CanvasIntegrationImpl (If I recall correctly), where it attempts to access an array at index 0 without verifying the array exists and is not empty.

[19mdavenport]

Probably both specifically during the CAS callback endpoint, which the browser treats as loading a page rather than an API call using javascript fetch