Allow for OpenSC variants on macOS

See ukf/ukf-meta#221.

macosx.properties

@@ -9,7 +9,16 @@
 #
 # Location of the PKCS#11 configuration file for OpenSC on Mac OS X.
 #
+# This varies depending on which version of OpenSC is installed.
+#
+# If the standard installer was used:
+#
 sign.uk.pkcs11Config = ${basedir}/mdx/uk/opensc-mac.cfg
+#
+# If the MacPorts system was used, override this by placing the following
+# definition in the local build.properties file:
+#
+#sign.uk.pkcs11Config = ${basedir}/mdx/uk/opensc-mac-macports.cfg
 
 #
 # Signing key alias within the keystore.

mdx/uk/opensc-mac-macports.cfg

@@ -0,0 +1,15 @@
+#
+# PKCS#11 provider configuration for for OpenSC running under Mac OS X
+#
+# Note: this configuration assumes that OpenSC has been installed using
+# the MacPorts system.
+#
+#    sudo port install opensc
+#
+# This version installs in /opt/local.
+#
+# If OpenSC has been installed using the standard installer, use opensc-mac.cfg
+# instead.
+#
+name = OpenSC
+library = /opt/local/lib/pkcs11/opensc-pkcs11.so

mdx/uk/opensc-mac.cfg

@@ -1,3 +1,16 @@
+#
 # PKCS#11 provider configuration for for OpenSC running under Mac OS X
+#
+# Note: this configuration assumes that OpenSC has been installed using
+# the standard installer as described here:
+#
+#    https://github.com/OpenSC/OpenSC/wiki/macOS-Quick-Start
+#
+# This version installs in /Library/OpenSC and /usr/local, and
+# includes a token driver.
+#
+# If OpenSC has been installed using MacPorts, use opensc-mac-macports.cfg
+# instead.
+#
 name = OpenSC
 library = /Library/OpenSC/lib/pkcs11/opensc-pkcs11.so