A quick and dirty way to authenticate users in a Sinatra app. Probably not secure.

sinatrauthentication.rb

require 'sinatra'
require 'sinatra/reloader' if development?
require 'digest/md5'
require 'haml'

# enable :sessions
use Rack::Session::Cookie, :key => 'rack.session', :path => '/', :secret => 'change_me'

auth_dir = "./auth"

configure :test do
  auth_dir = "./auth_test"
  unless Dir.exist? auth_dir
    Dir.mkdir auth_dir
  end
end

get '/' do
  if session[:name]
    @greeting = session[:name]
  else
    @greeting = "World"
  end
  haml :index
end

get '/login' do
  haml :login
end

post '/login' do
  file_path = "#{auth_dir}/#{params[:name]}.txt"
  if File.exist?(file_path) && params[:password]
    provided_password = Digest::MD5.hexdigest(params[:password].strip)
    correct_password = File.read(file_path)
    if provided_password == correct_password
      session[:name] = params[:name]
      redirect to '/'
    else
      "Invalid password."
    end
  else
    "You don't exist"
  end
end

get '/join' do
  haml :join
end

post '/join' do
  file_path = "#{auth_dir}/#{params[:name]}.txt"
  if !File.exist?(file_path) && params[:password]
    File.open(file_path, 'w') do |f|
      f.print Digest::MD5.hexdigest(params[:password].strip)
    end
    session[:name] = params[:name]
    redirect to '/'
  else
    "You already exist, or forgot to provide a password."
  end
end

get '/logout' do
  session.destroy
  redirect to '/'
end

__END__

@@ layout
%html
  %body
    = yield
    %br
    %ul.nav-menu{:style => "list-style-type: none;"}
      %li
        %a{:href => "/login"} Log In
      %li
        %a{:href => "/logout"} Log Out
      %li
        %a{:href => "/join"} Join

@@ index
= "Hello, #{@greeting}!"

@@ login
= "Log in here"
%form{:action => '/login', :method => 'post'}
  %input{:type => 'text', :name => 'name'}
  %input{:type => 'password', :name => 'password'}
  %input{:type => 'submit', :value => 'Log In'}

@@ join
= "Join Us."
%form{:action => '/join', :method => 'post'}
  %input{:type => 'test', :name => 'name'}
  %input{:type => 'password', :name => 'password'}
  %input{:type => 'submit', :value => 'Sign Up'}

sinatrauthentication_test.rb

require 'minitest/autorun'
require 'rack/test'

require './sinatrauthenticate.rb'

set :environment, :test

class SinatrauthenticateTest < MiniTest::Test
  include Rack::Test::Methods
  
  def app
    Sinatra::Application
  end
  
  def test_hello_world
    get '/'
    assert last_response.ok?
    assert_match /Hello, World!/, last_response.body
  end
  
  def test_login_page
    get '/login'
    assert last_response.ok?
    assert_match /Log in here/, last_response.body
  end
  
  def test_join_page
    get '/join'
    assert last_response.ok?
    assert_match /Join Us\./, last_response.body
  end
  
  def test_successful_login
    post '/join', :name => "Andrew", :password => "unsafe"
    post '/login', :name => "Andrew", :password => "unsafe"
    follow_redirect!
    assert_match /Hello, Andrew!/, last_response.body
  end
end