Added HTTP-based authentication

The purpose of this is in order to tie CalDAV accounts to an external web
application. This application must provide a URL end point to which a POST
request can be made, with the username/password sent as the payload. A 200 or
201 response is considered successful authentication. Any other response is
a failure.

config

@@ -77,6 +77,13 @@ pam_group_membership =
 # Path to the Courier Authdaemon socket
 courier_socket =
 
+# HTTP authentication request URL endpoint
+auth_url =
+# POST param to use for username
+user_param = username
+# POST param to use for password
+password_param = password
+
 
 [rights]
 # Rights management method