module ActionController
  module HttpAuthentication
    # Makes it dead easy to do HTTP Basic authentication.
    # 
    # Simple Basic example:
    # 
    #   class PostsController < ApplicationController
    #     USER_NAME, PASSWORD = "dhh", "secret"
    #   
    #     before_filter :authenticate, :except => [ :index ]
    #   
    #     def index
    #       render :text => "Everyone can see me!"
    #     end
    #   
    #     def edit
    #       render :text => "I'm only accessible if you know the password"
    #     end
    #   
    #     private
    #       def authenticate
    #         authenticate_or_request_with_http_basic do |user_name, password| 
    #           user_name == USER_NAME && password == PASSWORD
    #         end
    #       end
    #   end
    # 
    # 
    # Here is a more advanced Basic example where only Atom feeds and the XML API is protected by HTTP authentication, 
    # the regular HTML interface is protected by a session approach:
    # 
    #   class ApplicationController < ActionController::Base
    #     before_filter :set_account, :authenticate
    #   
    #     protected
    #       def set_account
    #         @account = Account.find_by_url_name(request.subdomains.first)
    #       end
    #   
    #       def authenticate
    #         case request.format
    #         when Mime::XML, Mime::ATOM
    #           if user = authenticate_with_http_basic { |u, p| @account.users.authenticate(u, p) }
    #             @current_user = user
    #           else
    #             request_http_basic_authentication
    #           end
    #         else
    #           if session_authenticated?
    #             @current_user = @account.users.find(session[:authenticated][:user_id])
    #           else
    #             redirect_to(login_url) and return false
    #           end
    #         end
    #       end
    #   end
    # 
    # Simple Digest example. Note the block must return the user's password so the framework 
    # can appropriately hash it to check the user's credentials. Returning nil will cause authentication to fail. 
    #  
    #   class PostsController < ApplicationController 
    #     Users = {"dhh" => "secret"} 
    #    
    #     before_filter :authenticate, :except => [ :index ] 
    #    
    #     def index 
    #       render :text => "Everyone can see me!" 
    #     end 
    #    
    #     def edit 
    #       render :text => "I'm only accessible if you know the password" 
    #     end 
    #    
    #     private 
    #       def authenticate 
    #         authenticate_or_request_with_http_digest(realm) do |user_name|  
    #           Users[user_name] 
    #         end 
    #       end 
    #   end
    #
    #
    # In your integration tests, you can do something like this:
    # 
    #   def test_access_granted_from_xml
    #     get(
    #       "/notes/1.xml", nil, 
    #       :authorization => ActionController::HttpAuthentication::Basic.encode_credentials(users(:dhh).name, users(:dhh).password)
    #     )
    # 
    #     assert_equal 200, status
    #   end
    #  
    #  
    # On shared hosts, Apache sometimes doesn't pass authentication headers to
    # FCGI instances. If your environment matches this description and you cannot
    # authenticate, try this rule in your Apache setup:
    # 
    #   RewriteRule ^(.*)$ dispatch.fcgi [E=X-HTTP_AUTHORIZATION:%{HTTP:Authorization},QSA,L]
    module Basic
      extend self

      module ControllerMethods
        def authenticate_or_request_with_http_basic(realm = "Application", &login_procedure)
          authenticate_with_http_basic(&login_procedure) || request_http_basic_authentication(realm)
        end

        def authenticate_with_http_basic(&login_procedure)
          HttpAuthentication::Basic.authenticate(self, &login_procedure)
        end

        def request_http_basic_authentication(realm = "Application")
          HttpAuthentication::Basic.authentication_request(self, realm)
        end
      end

      def authenticate(controller, &login_procedure)
        unless authorization(controller.request).blank?
          login_procedure.call(*user_name_and_password(controller.request))
        end
      end

      def user_name_and_password(request)
        decode_credentials(request).split(/:/, 2)
      end
  
      def authorization(request)
        request.env['HTTP_AUTHORIZATION']   ||
        request.env['X-HTTP_AUTHORIZATION'] ||
        request.env['X_HTTP_AUTHORIZATION'] ||
        request.env['REDIRECT_X_HTTP_AUTHORIZATION']
      end
    
      def decode_credentials(request)
        # Properly decode credentials spanning a new-line
        auth = authorization(request)
        auth.slice!('Basic ')
        ActiveSupport::Base64.decode64(auth || '')
      end

      def encode_credentials(user_name, password)
        "Basic #{ActiveSupport::Base64.encode64("#{user_name}:#{password}")}"
      end

      def authentication_request(controller, realm)
        controller.headers["WWW-Authenticate"] = %(Basic realm="#{realm.gsub(/"/, "")}")
        controller.__send__ :render, :text => "HTTP Basic: Access denied.\n", :status => :unauthorized
      end
    end
    
    module Digest
      extend self
    
      module ControllerMethods
        def authenticate_or_request_with_http_digest(realm = "Application", &password_procedure)
          begin 
            authenticate_with_http_digest!(realm, &password_procedure)
          rescue ActionController::HttpAuthentication::Error => e
            msg = e.message
            msg = "#{msg} expected '#{e.expected}' was '#{e.was}'" unless e.expected.nil?
            raise msg if e.fatal?
            request_http_digest_authentication(realm, msg)
          end
        end

        # Authenticate using HTTP Digest, throwing ActionController::HttpAuthentication::Error on failure.
        # This allows more detailed analysis of authentication failures
        # to be relayed to the client.
        def authenticate_with_http_digest!(realm = "Application", &login_procedure)
            HttpAuthentication::Digest.authenticate(self, realm, &login_procedure)
        end

        # Authenticate with HTTP Digest, returns true or false
        def authenticate_with_http_digest(realm = "Application", &login_procedure)
          HttpAuthentication::Digest.authenticate(self, realm, &login_procedure) rescue false
        end

        # Render output including the HTTP Digest authentication header
        def request_http_digest_authentication(realm = "Application", message = nil)
          HttpAuthentication::Digest.authentication_request(self, realm, message)
        end
        
        # Add HTTP Digest authentication header to result headers
        def http_digest_authentication_header(realm = "Application")
          HttpAuthentication::Digest.authentication_header(self, realm)
        end
      end

      # Raises error unless authentictaion succeeds, returns true otherwise
      def authenticate(controller, realm, &password_procedure)
        raise Error.new(false), "No authorization header found" unless authorization(controller.request)
        validate_digest_response(controller, realm, &password_procedure)
        true
      end

      def authorization(request)
        request.env['HTTP_AUTHORIZATION']   ||
        request.env['X-HTTP_AUTHORIZATION'] ||
        request.env['X_HTTP_AUTHORIZATION'] ||
        request.env['REDIRECT_X_HTTP_AUTHORIZATION']
      end

      # Raises error unless the request credentials response value matches the expected value.
      def validate_digest_response(controller, realm, &password_procedure) 
        credentials = decode_credentials(controller.request) 

        # Check the nonce, opaque and realm.
        # Ignore nc, as we have no way to validate the number of times this nonce has been used
        validate_nonce(controller.request, credentials[:nonce])
        raise Error.new(false, realm, credentials[:realm]), "Realm doesn't match" unless realm == credentials[:realm]
        raise Error.new(true, opaque(controller.request), credentials[:opaque]),"Opaque doesn't match" unless opaque(controller.request) == credentials[:opaque]

        password = password_procedure.call(credentials[:username])
        raise Error.new(false), "No password" if password.nil?
        expected = expected_response(controller.request.env['REQUEST_METHOD'], controller.request.url, credentials, password)
        raise Error.new(false, expected, credentials[:response]), "Invalid response" unless expected == credentials[:response]
      end 

      # Returns the expected response for a request of +http_method+ to +uri+ with the decoded +credentials+ and the expected +password+ 
      def expected_response(http_method, uri, credentials, password) 
        ha1 = ::Digest::MD5.hexdigest([credentials[:username], credentials[:realm], password].join(':')) 
        ha2 = ::Digest::MD5.hexdigest([http_method.to_s.upcase,uri].join(':')) 
        ::Digest::MD5.hexdigest([ha1,credentials[:nonce], credentials[:nc], credentials[:cnonce],credentials[:qop],ha2].join(':')) 
      end  

      def encode_credentials(http_method, credentials, password) 
        credentials[:response] = expected_response(http_method, credentials[:uri], credentials, password) 
        "Digest " + credentials.sort_by {|x| x[0].to_s }.inject([]) {|a, v| a << "#{v[0]}='#{v[1]}'" }.join(', ') 
      end 

      def decode_credentials(request) 
        authorization(request).to_s.gsub(/^Digest\s+/,'').split(',').inject({}) do |hash, pair| 
          key, value = pair.split('=', 2) 
          hash[key.strip.to_sym] = value.to_s.gsub(/^"|"$/,'').gsub(/'/, '') 
          hash 
        end 
      end 

      def authentication_header(controller, realm)
        controller.headers["WWW-Authenticate"] = %(Digest realm="#{realm}", qop="auth", algorithm=MD5, nonce="#{nonce(controller.request)}", opaque="#{opaque(controller.request)}") 
      end

      def authentication_request(controller, realm, message = "HTTP Digest: Access denied")
        authentication_header(controller, realm)
        controller.send! :render, :text => message, :status => :unauthorized
      end

      # Uses an MD5 digest based on time to generate a value to be used only once.
      #
      # A server-specified data string which should be uniquely generated each time a 401 response is made.
      # It is recommended that this string be base64 or hexadecimal data.
      # Specifically, since the string is passed in the header lines as a quoted string, the double-quote character is not allowed.
      #
      # The contents of the nonce are implementation dependent.
      # The quality of the implementation depends on a good choice.
      # A nonce might, for example, be constructed as the base 64 encoding of
      #
      # => time-stamp H(time-stamp ":" ETag ":" private-key)
      #
      # where time-stamp is a server-generated time or other non-repeating value,
      # ETag is the value of the HTTP ETag header associated with the requested entity,
      # and private-key is data known only to the server.
      # With a nonce of this form a server would recalculate the hash portion after receiving the client authentication header and
      # reject the request if it did not match the nonce from that header or
      # if the time-stamp value is not recent enough. In this way the server can limit the time of the nonce's validity.
      # The inclusion of the ETag prevents a replay request for an updated version of the resource.
      # (Note: including the IP address of the client in the nonce would appear to offer the server the ability
      # to limit the reuse of the nonce to the same client that originally got it.
      # However, that would break proxy farms, where requests from a single user often go through different proxies in the farm.
      # Also, IP address spoofing is not that hard.)
      #
      # An implementation might choose not to accept a previously used nonce or a previously used digest, in order to
      # protect against a replay attack. Or, an implementation might choose to use one-time nonces or digests for
      # POST or PUT requests and a time-stamp for GET requests. For more details on the issues involved see Section 4
      # of this document.
      #
      # The nonce is opaque to the client.
      def nonce(request, time = Time.now)
        session_id = request.is_a?(String) ? request : request.session.session_id
        t = time.to_i
        hashed = [t, session_id]
        digest = ::Digest::MD5.hexdigest(hashed.join(":"))
        Base64.encode64("#{t}:#{digest}").gsub("\n", '')
      end

      def validate_nonce(request, value)
        t = Base64.decode64(value).split(":").first.to_i
        raise Error.new(true), "Stale Nonce" if (t - Time.now.to_i).abs > 10 * 60
        n = nonce(request, t)
        raise Error.new(true, value, n), "Bad Nonce" unless n == value
      end

      # Opaque based on digest of session_id
      def opaque(request)
        session_id = request.is_a?(String) ? request : request.session.session_id
        @opaque ||= Base64.encode64(::Digest::MD5::hexdigest(session_id)).gsub("\n", '')
      end
    end

    class Error < RuntimeError
      attr_accessor :expected, :was
      def initialize(fatal = false, expected = nil, was = nil)
        @fatal = fatal
        @expected = expected
        @was = was
      end

      def fatal?; @fatal; end
    end
  end
end