Add support for development signing using SoftHSMv2 on macOS

See ukf/ukf-meta#221.

macosx.properties

@@ -28,6 +28,10 @@ sign.uk.pkcs11Config = ${basedir}/mdx/uk/opensc-mac.cfg
 # For a Yubikey, use this override in build.properties:
 #
 #sign.uk.pkcs11Config = ${basedir}/mdx/uk/yubikey-mac.cfg
+#
+# For the SoftHSMv2 soft token, use this override in build.properties:
+#
+#sign.uk.pkcs11Config = ${basedir}/mdx/uk/softhsm-mac-macports.cfg
 
 #
 # Signing key alias within the keystore.

mdx/uk/softhsm-mac-macports.cfg

@@ -0,0 +1,8 @@
+#
+# PKCS#11 provider configuration for for SoftHSM running under macOS.
+#
+# Note: this configuration assumes that SoftHSM has been installed using
+# the MacPorts system.
+#
+name = SoftHSM
+library = /opt/local/lib/softhsm/libsofthsm2.so