[CLEANUP] Code style of authentication classes

Clean up the source code of the authentication classes.
This patch does not change any functionality.
It serves as a basis for further improvements.

Resolves: #57788
Releases: 6.2
Change-Id: I555456c28da6697398a15ad9718a162f98aef61a
Reviewed-on: https://review.typo3.org/29322
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn