Add support for locating ykcs11 library on macOS

[ye4241]

This pull request enhances the way the getYkcs11Library() method in YubiKey.java locates the YubiKey PKCS#11 library, making it more flexible and robust, especially for custom and MacOS environments.

Improvements to library discovery:

• Added support for specifying a custom PKCS#11 library path via the PKCS11_MODULE environment variable, allowing users to override the default search logic.
• Improved MacOS support by searching multiple common locations for libykcs11.dylib, including paths from the DYLD_LIBRARY_PATH environment variable, increasing compatibility with different installation methods.

[ebourg]

Thank you for the suggestion. Do you know which Homebrew package provides libykcs11.dylib? I couldn't find it.

I'm not familiar with macOS, in which case is DYLD_LIBRARY_PATH used?

I'm not convinced by the PKCS11_MODULE environment variable, I tend to think that for a custom path to libykcs11 the best is to use the PKCS11 storetype with a standard SunPKCS configuration file specifying the path to the library.

Also keep in mind that you can replace the YUBIKEY storetype with PIV and simply ditch the ykcs11 library (in this mode Jsign bypasses the PKCS#11 library and talks to the Yubikey directly).

[ebourg]

Do you know which Homebrew package provides libykcs11.dylib? I couldn't find it.

Ok got it, it comes from the yubico-piv-tool formulae.

We could also add the Linux path: /home/linuxbrew/.linuxbrew/lib/libykcs11.so

[ye4241]

I'm not familiar with macOS, in which case is DYLD_LIBRARY_PATH used?

DYLD_LIBRARY_PATH is an environment variable in macOS, used to specify directories where the system should search for dynamic library (.dylib) files. It helps the operating system locate the necessary libraries during the execution of programs.

I'm not convinced by the PKCS11_MODULE environment variable, I tend to think that for a custom path to libykcs11 the best is to use the PKCS11 storetype with a standard SunPKCS configuration file specifying the path to the library.

Let me remove this logic first.