How can I check the Siebel Variable from the applet Request URL?

I am trying to add one request variable from Siebel Adapter for UCM and trying to catch the same in UCM custom filter.

My Customer wants the blockage to UCM access only to Siebel. But that variable is not being caught in the custom filter while opened in siebel applet . While I am typing the same in URL manually. It is printing the value to it.

Please anyone suggest.

Thanks