Shortest way to get Linkedin authorized access token

linkedin.rb

require 'sinatra'
require "sinatra/reloader" if development?
require 'http'
require 'json'

# https://www.linkedin.com/developers/apps
class Settings
  CLIENT_ID     = '...'
  CLIENT_SECRET = '...'
  ACCESS_TOKEN  = '...'
  URL           = 'http://your-app-url'
end

get '/' do
  url   = Settings::URL + '/auth'
  scope = 'r_liteprofile r_emailaddress'
  redirect "https://www.linkedin.com/oauth/v2/authorization?client_id=#{Settings::CLIENT_ID}&state=#{SecureRandom.uuid}&scope=#{scope}&redirect_uri=#{url}&response_type=code"
end

get '/auth' do
  uri = 'https://www.linkedin.com/oauth/v2/accessToken'

  request = {
    form: {
      grant_type:    'authorization_code',
      code:          params[:code],
      client_id:     Settings::CLIENT_ID,
      client_secret: Settings::CLIENT_SECRET,
      redirect_uri:  Settings::URL + '/auth'
    }
  }

  response = HTTP.post(uri, request)
  p response.parse
end

get '/positions' do
  response = HTTP
               .auth("Bearer #{Settings::ACCESS_TOKEN}")
               .get('https://api.linkedin.com/v2/me')
  user = JSON.parse(response.body)

=begin
  {
    "localizedLastName" => "Ibragimov",
    "profilePicture" => { "displayImage" => "urn:li:digitalmediaAsset:C5103AQFNr5ZVJMbOeA" },
    "firstName" => {
      "localized" => { "en_US" => "Renat" },
      "preferredLocale" => { "country" => "US", "language" => "en" }
    },
    "lastName" => {
      "localized" => { "en_US" => "Ibragimov" },
      "preferredLocale" => { "country" => "US", "language" => "en" }
    },
    "id" => "zxzQnHQpnU",
    "localizedFirstName" => "Renat"
  }
=end

  slim :positions, layout: false, locals: { user: user }
end

__END__

@@ positions
html
  head
    title MpaKus LinkedIn positions history
  body
    = user