[CORE-3636] validate certificates

[hemarkus]

also fixes lots of bugs!

Checklist

• [ ] Commits are reasonably small, easy to follow, and only concern one topic or task
• [ ] Commit messages are descriptive and include more details in the body if necessary
• [ ] Acceptance criteria including constraints are present in the ticket or linked
• [ ] There is no communication or clarifications that has not been added to the ticket
• [ ] No further unit tests need to be added or updated
• [ ] No further component test cases need to be adjusted
• [ ] The specification and documentation are up-to-date with the implementation
• [ ] Link to Pull Request is added to the ticket (Add Tickets to title)