A simple app that logs you into the captive WiFi automatically and can be run in background intelligently without draining your battery. It supports the latest Android 5.1.1, Android M (6.0 and 6.01) , Android N (7), Android M(8) and Android O
It has 10000 + paid downloads from Amazon and 15000+ from Google Play. AutoWiFi

A very frequent update you can tell from the last update is pretty close to today, it supports Android 5.x, lollipop.
have it's own way to detect the internet state other than generate_204

Whether you are connected to a company, hotel, or hospital guest network, you may need to type the username/password periodically. With WiFi Login, you only have to sign in once, and after that, it does it for you.
It will be waken up whenever there a WiFi state change, like when you walk between buildings and you don't use up any battery power. WiFi Login works with most Guest WiFi in airports, hotels, hospitals, restaurants, and shopping malls.
Other Options,
Load username/password from Dropbox,
Profile for each WiFi
By SSID or WiFi Name
Daily passport rotation.
HelloGuestWiFi
WiFi Web Login
User Manual, http://wifiweblogin.blogspot.com/


A list of several sites reported by satisfied customers that work well with this app:
Buffalo State University, Greenville Health System , Google Starbucks, HomeDepot Wifi, BT Wi-fi with Fon, XFINITY WiFi, TP-LINK_TRAVEL,nosotros,Denny's-Guest-WiFi, Optimum WiFi,Silicon Peaks
HSE.RU, Stanford Visitor WiFi,KSU, Buffalo.edu, GWireless, George Washington University,OSUMC Guest Internet ,mo.gov public wifi, Tesco WiFi, covidien-guest, CBIguest, Lisburn Free WiFi, IKEA-WIFI,TWC WiFi

UK sites: LSE, edinburgh.gov.uk

National University of Ireland WiFi, Universidade Federal De Santa Catarina UFSC

support most WiFi By Cisco ISE or Aruba, yowireless