Add OIDC acceptance tests

[peintnermax]

With these tests, OIDC relevant redirects will be tested. Start of every test is invoking the authorize endpoint which should result in different outcomes:

• select_account prompt should result in /accounts
• login prompt - no session available - should end up in an error stating no session was found
• login prompt - previously authenticated password user - should end up on the password page for reauthentication
• none prompt - no session available - error
• none prompt - previously authenticated password user - should end up in a valid callback
• no prompt - no session available - should redirect to /loginname
• no prompt - previously authenticated password user - should end up in a valid callback