Avoid module-level imports of oscrypt

[AdrianVollmer]

Let me take this opportunity to thank you for important work on many of your projects, some of which have become a corner stone of the OST community. Your efforts are very appreciated.

Today I'd like to discuss the oscrypto dependency. As you are aware, there are issues in some of your projects which depend on minikerberos (skelsec/pypykatz#136, skelsec/msldap#37) due to a bad regex if openssl has a double digit patch number. Currently, openssl-3.0.10 is the current version on Kali and Debian unstable and probably more. This is discussed here: wbond/oscrypto#78

I'm not sure why exactly the oscrypto dependency is needed, as cryptography is already a dependency due to the asysocks dependency. I think it could be replaced by cryptography, but unfortunately I lack the skills, time and motivation to do this.

To alleviate the issue, I propose to avoid the module-level imports of oscrypto and move them to the functions where they are needed by merging this PR. This would allow us to use projects like LdapRelayScan which need minikerberos, but not the pkinit module. Note that minikerberos has over 900 dependents (including forks, not sure how accurate this information is though), even though only 26 files (also including forks and identical files) actually import minikerberos.pkinit.

Still, if you manage to remove the oscrypto dependency, I'd count that as a win. What do you think?

The original commit message follows. Please note that I could not yet test this change.

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Many dependents of minikerberos don't need PKINIT, so it makes sense to import oscrypto only when needed. Especially because oscrypto<=1.3.0 does not work when openssl>=3.0.10.

See: wbond/oscrypto#78

[skelsec]

Please check the new version of asyauth it should fix this issue.

[AdrianVollmer]

Fantastic. Thank you!