ユーザからのID/PASS だけでOAuth 通過して、つぶやいてみる Ref: http://qiita.com/ikedahidenori/items/0088af5aec79b4b0008e

tw_oauth.rb

require 'oauth'
require 'oauth/consumer'
require 'twitter'
require 'mechanize'

# Set your Twitter ID/PASS
ID = 'id'
PASS = 'pass'

consumer_key = ENV['TWITTER_CONSUMER_KEY'] # Please set environment. or raw string
consumer_secret = ENV['TWITTER_SECRET']
consumer = OAuth::Consumer.new(
  consumer_key,
  consumer_secret,
  {site: 'https://api.twitter.com'}
)

request_token = consumer.get_request_token
uri = request_token.authorize_url

a = Mechanize.new {|agent|
  agent.user_agent_alias = 'Mac Safari'
}

oauth_action_uri = 'https://api.twitter.com/oauth/authorize'
pin_code = ''
a.get(uri) do |page|
  form = page.form_with(action: oauth_action_uri)
  # fill id/pass field up if not logged in.
  unless form.field_with(name: 'session[username_or_email]').nil? then
    form.field_with(name: 'session[username_or_email]').value = ID
  end
  unless form.field_with(name: 'session[password]').nil? then
    form.field_with(name: 'session[password]').value = PASS
  end
  button = form.button_with(value: /Authorize app/) # set submit button
  res = form.submit(button)
  pin_code = res.search('//*[@id="oauth_pin"]/p/kbd/code').text # set pin code
end

access_token = request_token.get_access_token(oauth_verifier: pin_code)

tw = Twitter::Client.new(
  consumer_key:       consumer_key,
  consumer_secret:    consumer_secret,
  oauth_token:        access_token.token,
  oauth_token_secret: access_token.secret
)

tw.update 'tweet' # Update status