Kleides-mfa

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* Configure ValidationService on the database that is being migrated.

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* Send user_login_failed signal on device failures.
* Test Django login signals with Kleides MFA.

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* Add python 3.8 and Django 3.1 to support matrix.
* Test unprintable token input.
* Remove future statements.
* Remove non-optional PATCH_USER setting.

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* Fix unset plugin attribute on PermissionDeniedError.

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* Restart authentication when accessing a bad device.

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* Replace deprecated Django-3.0 functions.
* Fix session cleanup after login as different user.