Migrate FrontendUserAuthentication and rewrite failing
unit tests for FlashMessageQueue as functional tests

Resolves: #77330
Releases: master
Change-Id: Ib109bddc1a4b1272c179a0e2ff41363462c3b5e7
Reviewed-on: https://review.typo3.org/49284


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>