allows alternative configuration file

bin/account-manager.cgi.in

@@ -9,7 +9,9 @@ use Config::Tiny;
 
 use AccountManager::WebRequest;
 
-my $configuration = Config::Tiny->read('@sysconfdir@/manager.conf');
+my $configuration_file =
+    $ENV{ACCOUNTMANAGER_CONFIG} || '@sysconfdir@/manager.conf';
+my $configuration = Config::Tiny->read($configuration_file);
 
 my $request = AccountManager::WebRequest->new(
     configuration => $configuration