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)
It has 10000 + paid downloads from Amazon and 9000+ 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_TRAVELnosotrosDenny's-Guest-WiFi Optimum WiFiSilicon Peaks
HSE.RU Stanford Visitor WiFiKSU Buffalo.edu GWireless George Washington UniversityOSUMC Guest Internet mo.gov public wifi Tesco WiFi covidien-guest CBIguest Lisburn Free WiFi IKEA-WIFITWC 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