#MODEL

require 'bcrypt'

class User
  include DataMapper::Resource

  property :id, Serial
  property :email, String
  property :name, String
  property :username, Text
  property :password_digest, Text

  has n, :peeps, :through => Resource

  def password=(password)
    self.password_digest = BCrypt::Password.create(password)
  end

end

.
.
.

#CONTROLLER

class Chitter < Sinatra::Base

get '/login' do
    erb :login
  end

  post '/login' do
    user = User.first(username: params[:username])
    if BCrypt::Password.new(user.password_digest) == params[:password]
      session[:user] = user.id
      redirect '/loggedin'
    else
      flash.now[:fail] = 'Password incorrect - please try again'
      erb :login
    end
  end

end

.
.
.

#VIEW

#login.erb

<form action='/login' method='post'>
  User Handle: <input type="text" name="username" value="username">
  Password: <input type="password" name="password" value="password">
  <input type="submit" name="Login" value="Login">
</form>

<% if flash[:fail] %>
  <%= flash[:fail] %>
<% end %>