In Sierra a new smart card component has been introduced: pam_smartcard. PAM is Pluggable Authentication Modules.

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• A: The software is compatible with Mac OS X 10.13 High Sierra. B: The software has limited functionality with Mac OS X 10.13 Hgh Sierra. C: The software is not compatible with Mac OS X 10.13 High Sierra.
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The source code is available at macOS 10.12 Source and is part of the pam_modules component.

pam_smartcard

The pam_smartcard(8) manage is:
I guess this is related to the introduction of the native support of PIV cards in Sierra. See 'macOS Sierra and PIVToken source code'.
The pam_smartcard PAM module is used by two services by default:

• authorization_ctk
• screensaver_ctk

SmartCardServices

Another interesting man page is SmartCardServices(7). Here is an extract:

PAM PKCS#11?

Since PAM is available in macOS maybe the PAM PKCS#11 module can be used without too much changes? This module is for GNU/Linux but may be adapted for macOS.

Cac Reader For Macbook

In this case, adding support for smart card login in macOS, if you already have a PKCS#11 library for your card, should be easy.

Conclusion

The use of smart card in macOS for high level services (like authentication) is easier in Sierra, at least for PIV smart cards.

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I imagine that the support of other smart cards models will be proposed by third parties 'soon'.