Add authorization header per backend

Help!
1

I want to add an autorization header per backend, it’s possible?
I already try this but is not working

backend default_ad_agent
        mode http
        http-request add-header Authorization "xxxx" if { srv_id 1 }
        http-request add-header Authorization "yyyy" if { srv_id 2 }
        server 192.168.60.32 192.168.60.32:8080 id 1 weight 1 maxconn 10000 check inter 60000 rise 2 fall 3
        server 192.168.60.31 192.168.60.31:8080 id 2  weight 1 maxconn 10000 check inter 60000 rise 2 fall 3