fix: idp logout issues

[JammingBen]

Description

Fixes falsely showing the logout page after opening ownCloud Web with an expired token. The issue seemed to be related to the fact that we manually logged out the user after token expiry, whereas the correct way is to let the IDP auth flow handle this. There is no need for a custom implementation on our side.

Also removes the threshold because it doesn't really make sense IMO. Either the token is expired, or it's still valid.

Related Issue

• refs https://github.com/owncloud/enterprise/issues/6639
• refs https://github.com/owncloud/enterprise/issues/6560
• refs https://github.com/owncloud/enterprise/issues/6627

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests
• Documentation
• Maintenance (e.g. dependency updates or tooling)

[JammingBen]

@kulmann @dschmidt Pinging you 2 for review since you got the most knowledge about IDP stuff. I'm still not 100% sure about the solution, but it looks good to me and seems to work.

[kulmann]

Nice finding 💪

[dschmidt]

LGTM (i guess)