Simple ruby class that allows to login to Facebook via HTTP client. This is for educational purposes only, you should always use the official API.

facebook-login.rb

require 'rest_client'
require 'nokogiri'

class FacebookLogin
  def initialize(username, password)
    @cookies = {}
    @payload = {email: username, pass: password}
    @headers = {'User-Agent' => 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.133 Safari/537.36'}
    # Define login flow
    @login_steps = [
        {
            url: 'https://mbasic.facebook.com/',
            method: 'GET',
            collect: [
                {xpath: 'input[@name="lsd"]', target: 'value', name: 'lsd'},
                {xpath: 'input[@name="m_ts"]', target: 'value', name: 'm_ts'},
                {xpath: 'input[@name="li"]', target: 'value', name: 'li'}
            ]
        },
        {
            url: 'https://mbasic.facebook.com/login.php?refsrc=https%3A%2F%2Fmbasic.facebook.com%2F&lwv=100&login_try_number=1&refid=8',
            method: 'POST'
        }
    ]
  end

  # Global request sender for POST/GET requests
  def send_request(url, method, headers = {}, cookies = {}, payload = {})
    begin
      response = ''
      RestClient::Request.execute(
          url: url,
          method: method,
          timeout: 20,
          headers: headers,
          cookies: cookies,
          payload: payload
      ) do  |resp, req, result, &block|
        # Handle redirection after login
        if [301, 302, 307].include? resp.code
          redirect_url =  resp.headers[:location]
          @cookies = resp.cookies || @cookies
          response = send_request(redirect_url, 'GET', headers, @cookies)
        else
          response = resp
        end
      end
      @cookies = response.cookies || @cookies
    rescue Exception => e
      puts e
      response = nil
    end
    return response
  end

  # Collect relevant request payload data from page HTML
  def collect_data_from_page(html, rules)
    doc = Nokogiri::HTML(html)
    rules.each do |collection_rule|
      xpath = collection_rule[:xpath]
      name = collection_rule[:name]
      target_element = doc.at(xpath)
      value = target_element.attr(collection_rule[:target])
      @payload[name] = value
    end
    @payload
  end

  # Get Facebook URLs when logged in
  def get(url)
    send_request(url, 'GET', @headers, @cookies)
  end

  def login
    # Iterate through all login flow steps
    result = ''
    @login_steps.each do |step|
      url = step[:url]
      method = step[:method]
      collection_rules = step[:collect]

      # Add payload if needed
      payload = method == 'POST' ? @payload : {}

      result = send_request(url, method, @headers, @cookies, payload)
      if collection_rules
        # Collect rules present in current step, collect data from page
        collect_data_from_page(result, collection_rules)
      end
    end
    result.match('logout.php') ? true : false
  end
end

# Usage example (be sure to change user and pass)
fb = FacebookLogin.new('mymailbox@lazyinbox.us', 'qwertyasdf')
if fb.login
  # Login success, do your thing
  puts fb.get('https://www.facebook.com/JimiHendrix/')
else
  puts 'Login Failed'
end