Perhaps you have free WiFi access, but need to click a button on a web page accepting terms and conditions... not a problem for a human, but not as easy to do programmatically.
This is some initial code for the ESP8266 to connect to a visitor WiFi hotspot, created in Visual Studio with the Visual Micro add-in.
Created for use in the DesktopDashboard project. https://github.com/gojimmypi/DesktopDashboard