Add logic and test for `\login` failure

[maxachis]

Context

Currently, the /login endpoint returns a generic 500 Internal Server Error message on a failed login, and there is no test for an invalid login. Let's fix that!

Requirements

• Update login to provide a more detailed response with an UNAUTHORIZED HTTP Status code
• Update documentation in resources page
• Add integration test to test for this.

Tests

• Add integration test as described above

Docs

• Update documentation in resources page

Open questions

• No open question