Tracking issue for tests

[Erik1000]

I have currently no time to add good tests. Especially the tests involving crypto need special attention and time.

We would need tests for:

• [ ] user id and user attribute removal
• [x] key validation (if there are really keys for all operations)
• [ ] Certificate if it handles secret and non-secret material correctly
• [x] key policy (if really only curve 25519 suite is accepted and if unencrypted secret key material is rejected)
• [ ] challenge signature checks
• [ ] that refresh tokens are really denied after a use (this is probably pain to test, because it needs database I/O)
• [ ] that the check constraint in the database really rejects invalid names (pain to check too because of database I/O)
• [ ] certification pagination test (if the order is as expected, has_next/previous is correct, after/before work as expected)