OAuth2 Sinatra Proxy App

server.rb

require 'sinatra'
require 'json'
require 'faraday'
require 'faraday_middleware'
 
enable :sessions
 
IDENTIFIER = "YOUR_IDENTIFIER"
SECRET = "YOUR_SECRET"
REDIRECT_URI = "http://localhost:3000/auth"
AUTH_URL = "https://api.harvestapp.com/oauth2/authorize"
TOKEN_URL = "https://api.harvestapp.com/oauth2/token"
BASE_API_URL = "https://api.harvestapp.com/"

# Middlware to insert "Accept: application/json" header
class JsonMiddleware < Faraday::Middleware
  def call(env)
    env[:request_headers]["Accept"] = "application/json"
    @app.call(env)
  end
end

# Redirect to the API to start the OAuth handshake
# http://www.getharvest.com/api/authentication-oauth2
# http://tools.ietf.org/html/draft-ietf-oauth-v2-22#section-4.1
get "/" do
  query_string = Rack::Utils.build_query({
    :client_id => IDENTIFIER,
    :redirect_uri => REDIRECT_URI,
    :state => "optional-csrf-token",
    :response_type => "code"
  })

  redirect "#{AUTH_URL}?#{query_string}"
end

# Harvest will redirect back here with the OAuth code you
# use to get the access token.
get "/auth" do
  query_string = Rack::Utils.build_query({
    :code => params[:code],
    :client_id => IDENTIFIER,
    :client_secret => SECRET,
    :redirect_uri => REDIRECT_URI,
    :grant_type => "authorization_code"
  })

  response = Faraday.post("#{TOKEN_URL}?#{query_string}")
  session[:token] = JSON.parse(response.body)["access_token"]
  redirect "/token"
end

# Removes favicon warnings
get "/favicon.ico" do
end

# Display your access token
get "/token" do
  session[:token]
end

# Proxy everything after / to Harvest
#
# http://localhost:3000/projects/1/entries?from=2013-01-10&to=2013-01-14
# => https://api.harvest.com/projects/1/entries?from=2013-01-10&to=2013-01-14
get "/*" do
  headers "Content-Type" => "text/plain"

  params.delete("captures")
  url = "/#{params.delete("splat").join}?"
  url += Rack::Utils.build_query(params)

  client = Faraday.new(:url => BASE_API_URL) do |faraday|
    faraday.request :url_encoded
    faraday.request :oauth2, session[:token]
    faraday.use JsonMiddleware
    faraday.adapter Faraday.default_adapter
  end

  response_body = client.get(url).body
  JSON.pretty_generate(JSON.parse(response_body))
end