Open a website link on connecting WIFI

I want to do an action when a mobile device is connected to my WIFI network.Like opening a URL on the connected device's browser or broadcasting a message.

Broadcasting a message is not possible without an App I guess. Refer this question . And I don't want users to install any custom app either developed by I or any third party to receive a broadcast message. Opening a link on connecting an SSID looks very simple when asking, but I am not able to find any online sources to do so.

I don't want an implementation. I just want a right direction to learn how to do these things if possible.

Any help is appreciated.