Add missing authority properties; add header note

Signed-off-by: Pekka Helenius <fincer89@hotmail.com>

bookstore/src/main/resources/authentication.properties

@@ -1,4 +1,21 @@
 # Pekka Helenius <fincer89@hotmail.com>, Fjordtek 2020
 
+# NOTE:
+#   These properties represent internal application properties,
+#   NOT linguistic front-end message strings. Never refer to keys
+#   in this file in your application front-end messages.
+#   These keys are accessible in Spring Environment context.
+
+
+
+# Login form authentication fields
+#
 auth.field.username     = b_username
-auth.field.password     = b_password
+auth.field.password     = b_password
+
+# User roles (authorities)
+#
+auth.authority.admin    = ADMIN
+auth.authority.helpdesk = HELPDESK
+auth.authority.sales    = MARKETING
+auth.authority.user     = USER