Manipulation for login page of Server response

Hello,

Requirement : End user should hit my company's portal"https://abc.com/shop/" & f5 should act as reverse proxy & forward the request to third party portal "https://xyz.com/shop/".

Problem : I could replace the host from request & send to the backend server which has been hosted on internet. Server responds with login page which has username, password text boxes & Login button. When end user clicks on login button it gets redirected to third party portal "https://xyz.com/shop/". While analyzing the source code of webpage it was found that under form tag of html page there is action tag which points it to "https://xyz.com/shop/". I tried stream expression in server response as mentioned below when HTTP_RESPONSE {

STREAM::disable STREAM::expression {@action=}

STREAM::enable log local0. "Stream Expression Replaced" } I could see the"Stream Expression Replaced" in LTM logs however when I click on login button, it goes to https://xyz.com/shop instead of https://abc.com/shop. Even after steam expression applied, I still see action=https://xyz.com/shop in source for server response. Please suggest how do I intercept server response in order to manipulate action under form tab.

Thanks in advance.