IITK firewall authentication script that uses nothing except for curl. It is possible to specify an interface manually (for compatibility with some unix systems). In case the user is already logged in, it can even force a logout to get the authentication page.

auth.sh

#!/bin/sh -eu
# Copyright 2017 Pallav Agarwal
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

firewall_url="https://172.31.1.251:1003"
ironport1_ip="172.22.1.1:3128"
ironport2_ip="172.22.1.2:3128"
example_url="http://93.184.216.34" 

# To reduce dependencies, replace this line below with the interface
# name like 'eth0' or 'enp9s0'
interface="$(route | grep '^default' | grep -o '[^ ]*$')"
printf "Username: "; read username
printf "Password: "; read password

url_encode() {
    local word="${1}"; shift
    local dataLength="${#word}"
    local index
    for ((index = 0; index < dataLength; index++)); do
        local char="${word:index:1}"
        case "${char}" in
            [a-zA-Z0-9.~_-])
                printf "${char}"
                ;;
            *)
                printf "%%%02X" "'${char}"
                ;;
        esac
    done
}

ironport() {
    for i in 1 2; do
        local name="ironport${i}_ip"
        eval local url='${'$name'}'
        local output="$(curl --silent --include \
            --proxy "http://${username}:${password}@${url}/" \
            "${example_url}" | head -1 | grep -o "407" )"
        if [ "${output}" == "407" ]; then
            echo "Unable to login to ironport${num}"
        fi
    done
}

get_login_page() {
    local output="$(curl --silent \
        --interface "${interface}" -k "${firewall_url}/logout?")"
    echo "${output}" | grep -oE '"htt[^"]*"' | grep -oE 'http[^"]*' 
}

get_magic() {
    local login_page="${1}"; shift
    local output="$(curl --silent \
        --interface "${interface}" -k "${login_page}")"
    local quoted="$(echo "${output}" | grep -oE \
        '"magic" value="[^"]*"' | grep -oE '"[^"]*"$')"
    echo "${quoted}" | grep -oE '[^"]*'
}

do_login() {
    local magic="${1}"; shift
    local output="$(curl -k --interface "${interface}" -X POST --silent \
        -d "username=${username}" \
        -d "password=${password}" \
        -d "magic=${magic}" \
        -d "submit=Continue" \
        "${firewall_url}/" )"
    echo "${output}" | grep -oE 'http[^"]*logout[^"]*'
    echo "${output}" | grep -oE 'http[^"]*keepalive[^"]*'
}

log_out() {
    local url="${1}"; shift
    curl -k --interface "${interface}" --silent "${url}"
}

keep_alive() {
    local url="${1}"; shift
    echo "Keepalive url is" "${url}"
    while :; do
        local output="$(curl -k -silent --interface "${interface}" "${url}")"

        ironport # Run ironport login too
        if echo "${output}" | grep -q "leave it open"; then
            echo "Keepalive successful"
            sleep 10
        else
            echo "Keepalive unsuccessful; Trying to get login screen"
            break
        fi
    done
}

main() {
    local output="${1}"; shift
    logout_url=$(echo "$output" | head -1)
    keepalive_url=$(echo "$output" | tail -1)

    echo "${logout_url}"
    echo "${keepalive_url}"

    ironport # Run ironport login too
    keep_alive "${keepalive_url}"
}

while :; do
    lpage="$(get_login_page)"
    magic="$(get_magic "${lpage}")"
    lurls="$(do_login "${magic}")"
    main "${lurls}"
    sleep 1
done