I see that if I did a long touch over a Wifi network, I can specify some proxy settings. In my company we use a Isa Proxy server, and each user has to login through domain server.
Is there any way to configure that on our tablets? ( Android 4.1)
There are multiple solutions. As you have Android 4.x, long-pressing on a WiFi APN in Settings→Networks & Wireless→WiFi lets you edit an APN. Check the "Advanced" box, and you can configure the proxy. Though this form does not offer separate fields for username/password, here's a trick how to do it:
For the server name, enter
user:pass@proxyserver (e.g. if the proxy is
10.11.12.1, user joe, password foo:
joe:firstname.lastname@example.org) -- this is how it works in some browsers for password-protected urls. In case this makes trouble (should not, but who knows), further details can be found at Android-Proxy.Blogspot.DE (don't be irritated by .DE, it's in English).
Another possibility would require your device to be rooted: ProxyDroid offers some comfort in connection with proxies. Next to supporting multiple profiles, it is also capable of handling different authentication methods.
You can use the Drony application to authenticate with your proxy.