[Help] How to redirect Login to another server roundcube mail

[doby nurcahyo <f.doby.n@xxxxxxxxx>]

Hii All,

On my server webmail is running roundcube at ip 172.18.4.21 with login
page roundcube itself .
I have intranet web php on ip 172.18.4.22, at this server intranet, I
make login php with submit button and it not same on login roundcube.

My big problem is, how to make intranet login username & password
directly log-in on server mail ?.

Thanks before guys..