server.on( "/", handleRoot);
...
}
 
/*F********************************************************************
*
**********************************************************************/
void 
handleRoot() 
{
	if( server.hasArg( "ssid" ) && server.hasArg( "password" )) 	
	{
		String ssid = server.arg( "ssid" );
		String password = server.arg( "password" );
		// Do next steps here
		...
		... 
	}
	else 
	{
	// If one of the creds is missing, go back to form page
		server.send( 200, "text/html", INDEX_HTML );
	}
}

Enter your WiFi credentials