Add ability to verify Yubikey second factor, list second factors

Dep: https://github.com/SURFnet/Stepup-Middleware-clientbundle/pull/4

The identity ID is currently hard-coded to `45fb401a-22b6-4829-9495-08b9610c18d4`. This identity must be present in the middleware.

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This is a check that belongs in the firewall, if the firewall decides to use another token that's fine. Not something the controller should be concerned with.