EW-649: Refactoring of authentication.

[mkreuzkam-cap]

Description

• Move classes which are not strategies to helper folder
• Check todos
• Add comments to explain unused variables
• Add typeguard for user
• Change type of bruteforce error
• Restructure some code

Links to Tickets or other pull requests

• https://ticketsystem.dbildungscloud.de/browse/EW-649

Approval for review

• DEV: If api was changed - generate-client:server was executed in vue frontend and changes were tested and put in a PR with the same branch name.
• QA: In addition to review, the code has been manually tested (if manual testing is possible)
• All points were discussed with the ticket creator, support-team or product owner. The code upholds all quality guidelines from the PR-template.

Notice: Please remove the WIP label if the PR is ready to review, otherwise nobody will review it.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud