[Bug Report]: OIDC token failures fail to notify upon errors #3264

Describe the Bug

Errors during ID token validation fail to notify back to the user.
This is due to an extra redirect in the path

• GET /oidc/callback
  • Exception, Sets error then redirects to /
• GET /
  • Not authed, Redired to /login
  • Flashed session lost
• GET /login

Steps to Reproduce

Setup OIDC with:

OIDC_ISSUER_DISCOVER=false
OIDC_PUBLIC_KEY=https://example.com

Expected Behaviour

"ID token validate failed with error: Failed to read signing key with error: Unexpected type of key value provided" message should display to user.

Exact BookStack Version

v21.12.5

PHP Version

No response

Hosting Environment

Dev

• Could do with cleaning up OpenIdConnectException usage while at it. Probably keep to normal exception then convert at controller level.
• Ensure case added to tests.