Bug 28786: (QA follow-up) Check the returned CSRF token

Bug 28786: (QA follow-up) Check the returned CSRF token

We're doing this in the registering stage and at disabling.

Test plan:
Ënable two-factor auth but logout/login on another tab. You should
get the Wrong CSRF token when submitting.
Do similar thing while disabling.
Verify that you can register / disable when in the same session.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>