Back to sync in auth handlers

[lucagobbi]

Description

Removed async stuff from BaseAuthHandler and other methods that were not using real async stuff. This is a breaking change since async custom auth handlers implementation needs to migrate to sync one.

Will update docs and blog after merging it in main.

Related to issue #958

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas

[valentimarco]

https://tenor.com/view/rip-juice-cry-cat-kitten-tears-gif-15751834

[pieroit]

@lucagobbi thanks!
@valentimarco I still do not understand why async is so cool and why we should deal with the complexity, while we run already in the damn threadpool XD