SCCM: only set preferred_auth when Kerberos is selected

Author: erdragone430

lib/msf/core/exploit/remote/http/sccm.rb

@@ -77,9 +77,11 @@ def get_secret_policies(http_opts, management_point, site_code, key, cert, sms_i
             opts = http_opts.merge({
               'uri' => '/ccm_system/request',
               'method' => 'CCM_POST',
-              'data' => message.to_s,
-              'preferred_auth' => datastore['HTTP::Auth'] == Msf::Exploit::Remote::AuthOption::KERBEROS ? 'Kerberos' : nil
+              'data' => message.to_s
             })
+            if datastore['HTTP::Auth'] == Msf::Exploit::Remote::AuthOption::KERBEROS
+              opts['preferred_auth'] = 'Kerberos'
+            end
             opts['headers'] = opts['headers'].merge({
               'Content-Type' => 'multipart/mixed; boundary="aAbBcCdDv1234567890VxXyYzZ"'
             })