[SSO UIA] force enter credentials for the re-authentication usecases

This issue has been migrated from [#9309](https://github.com/matrix-org/synapse/issues/9309).

---

When using password flow and performing some important actions (add email, delete device, deactivate account, upload signing keys) clients will require the user to enter his password again.

But currently when using SSO, the UIA flow will open the browser where you are already logged in. So you just have to tap the button to confirm the important action (no credentials required).

TLDR; you better lock your screen when using SSO