[TASK] Cleanup openid extension

Cleanup remaining CGL issues after namespace change.
Implement some best practices like strict string comparison
or dependency injection pattern where appropriate.

Last but not least make use of use statements for frequently
used class names.

Resolves: #48522
Releases: 6.2
Change-Id: I1f03d2fdf53ea7be42455663b36af56bc479fa21
Reviewed-on: https://review.typo3.org/21035
Reviewed-by: Wouter Wolters
Reviewed-by: Susanne Moog
Tested-by: Susanne Moog
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn