Remove some http_response_code()/exit()/die() usages

[cedric-anne]

Checklist before requesting a review

• I have read the CONTRIBUTING document.
• I have performed a self-review of my code.

Description

Follows #18046 .

Usage of the http_response_code() method is not compatible with many Symfony features (as explained in #18014) and usage of the exit()/die() methods prevents some Symfony features to be used (e.g. kernel events listeners).

I replace some usages of these methods to make the corresponding code fully compatible with the Symfony framework.

[trasher]

As discussed on our internal chat, there are some things to fix

[Pierstoval]

Responses miss the HTTP code from the Exception objects

[cedric-anne]

This page just displays a message indicating why authentication fails and a link to the login form. We could return a 400 error, but a 200 seems OK too. The authentication error could be related to many possible issues (unavailability of a remote system, bad credentials, ...) and would not always correspond to a bad request.

Anyway, it does not change much for the end user.

[Pierstoval]

It's perfectly fine to return a 4xx response that has HTML content with error messages, I'd even say it's recommended for clarity.
An HTTP 200 with an error message inside sounds like an "Error failed successfully" message 🤔

[cedric-anne]

I am not sure 400 matches the different cases, but it is probably the more generic 4xx code that could be used.