module ActionController::HttpAuthentication::Digest - actionpack-4.2.4 Documentation

# module ActionController::HttpAuthentication::Digest

Makes it dead easy to do HTTP Digest authentication.

### Simple Digest example¶ ↑

    require 'digest/md5'
    class PostsController < ApplicationController
      REALM = "SuperSecret"
      USERS = {"dhh" => "secret", #plain text password
               "dap" => Digest::MD5.hexdigest(["dap",REALM,"secret"].join(":"))}  #ha1 digest password

      before_action :authenticate, except: [:index]

      def index
        render plain: "Everyone can see me!"
      end

      def edit
        render plain: "I'm only accessible if you know the password"
      end

      private
        def authenticate
          authenticate_or_request_with_http_digest(REALM) do |username|
            USERS[username]
          end
        end
    end

### Notes¶ ↑

The `authenticate_or_request_with_http_digest` block must return the user's password or the ha1 digest hash so the framework can appropriately hash to check the user's credentials. Returning `nil` will cause authentication to fail.

Storing the ha1 hash: MD5(username:realm:password), is better than storing a plain password. If the password file or database is compromised, the attacker would be able to use the ha1 hash to authenticate as the user at this `realm`, but would not have the user's password to try using at other sites.

In rare instances, web servers or front proxies strip authorization headers before they reach your application. You can debug this situation by logging all environment variables, and check for HTTP_AUTHORIZATION, amongst others.

### Public Instance Methods

authenticate(request, realm, &password_procedure) click to toggle source

Returns false on a valid response, true otherwise

    # File lib/action_controller/metal/http_authentication.rb, line 189
    def authenticate(request, realm, &password_procedure)
      request.authorization && validate_digest_response(request, realm, &password_procedure)
    end

authentication_header(controller, realm) click to toggle source

    # File lib/action_controller/metal/http_authentication.rb, line 247
    def authentication_header(controller, realm)
      secret_key = secret_token(controller.request)
      nonce = self.nonce(secret_key)
      opaque = opaque(secret_key)
      controller.headers["WWW-Authenticate"] = %Q(Digest realm="#{realm}", qop="auth", algorithm=MD5, nonce="#{nonce}", opaque="#{opaque}")
    end

authentication_request(controller, realm, message = nil) click to toggle source

    # File lib/action_controller/metal/http_authentication.rb, line 254
    def authentication_request(controller, realm, message = nil)
      message ||= "HTTP Digest: Access denied.\n"
      authentication_header(controller, realm)
      controller.status = 401
      controller.response_body = message
    end

decode_credentials(header) click to toggle source

    # File lib/action_controller/metal/http_authentication.rb, line 240
    def decode_credentials(header)
      ActiveSupport::HashWithIndifferentAccess[header.to_s.gsub(/^Digest\s+/, '').split(',').map do |pair|
        key, value = pair.split('=', 2)
        [key.strip, value.to_s.gsub(/^"|"$/,'').delete('\')]
      end]
    end

decode_credentials_header(request) click to toggle source

    # File lib/action_controller/metal/http_authentication.rb, line 236
    def decode_credentials_header(request)
      decode_credentials(request.authorization)
    end

encode_credentials(http_method, credentials, password, password_is_ha1) click to toggle source

    # File lib/action_controller/metal/http_authentication.rb, line 231
    def encode_credentials(http_method, credentials, password, password_is_ha1)
      credentials[:response] = expected_response(http_method, credentials[:uri], credentials, password, password_is_ha1)
      "Digest " + credentials.sort_by {|x| x[0].to_s }.map {|v| "#{v[0]}='#{v[1]}'" }.join(', ')
    end

expected_response(http_method, uri, credentials, password, password_is_ha1=true) click to toggle source

Returns the expected response for a request of `http_method` to `uri` with the decoded `credentials` and the expected `password` Optional parameter `password_is_ha1` is set to `true` by default, since best practice is to store ha1 digest instead of a plain-text password.

    # File lib/action_controller/metal/http_authentication.rb, line 221
    def expected_response(http_method, uri, credentials, password, password_is_ha1=true)
      ha1 = password_is_ha1 ? password : ha1(credentials, password)
      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

ha1(credentials, password) click to toggle source

    # File lib/action_controller/metal/http_authentication.rb, line 227
    def ha1(credentials, password)
      ::Digest::MD5.hexdigest([credentials[:username], credentials[:realm], password].join(':'))
    end

nonce(secret_key, time = Time.now) click to toggle source

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, PUT, or PATCH 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. Composed of Time, and hash of Time with secret key from the Rails session secret generated upon creation of project. Ensures the time cannot be modified by client.

    # File lib/action_controller/metal/http_authentication.rb, line 299
    def nonce(secret_key, time = Time.now)
      t = time.to_i
      hashed = [t, secret_key]
      digest = ::Digest::MD5.hexdigest(hashed.join(":"))
      ::Base64.strict_encode64("#{t}:#{digest}")
    end

opaque(secret_key) click to toggle source

Opaque based on random generation - but changing each request?

    # File lib/action_controller/metal/http_authentication.rb, line 318
    def opaque(secret_key)
      ::Digest::MD5.hexdigest(secret_key)
    end

secret_token(request) click to toggle source

    # File lib/action_controller/metal/http_authentication.rb, line 261
    def secret_token(request)
      key_generator  = request.env["action_dispatch.key_generator"]
      http_auth_salt = request.env["action_dispatch.http_auth_salt"]
      key_generator.generate_key(http_auth_salt)
    end

validate_digest_response(request, realm, &password_procedure) click to toggle source

Returns false unless the request credentials response value matches the expected value. First try the password as a ha1 digest password. If this fails, then try it as a plain text password.

    # File lib/action_controller/metal/http_authentication.rb, line 196
    def validate_digest_response(request, realm, &password_procedure)
      secret_key  = secret_token(request)
      credentials = decode_credentials_header(request)
      valid_nonce = validate_nonce(secret_key, request, credentials[:nonce])

      if valid_nonce && realm == credentials[:realm] && opaque(secret_key) == credentials[:opaque]
        password = password_procedure.call(credentials[:username])
        return false unless password

        method = request.env['rack.methodoverride.original_method'] || request.env['REQUEST_METHOD']
        uri    = credentials[:uri]

        [true, false].any? do |trailing_question_mark|
          [true, false].any? do |password_is_ha1|
            _uri = trailing_question_mark ? uri + "?" : uri
            expected = expected_response(method, _uri, credentials, password, password_is_ha1)
            expected == credentials[:response]
          end
        end
      end
    end

validate_nonce(secret_key, request, value, seconds_to_timeout=5*60) click to toggle source

Might want a shorter timeout depending on whether the request is a PATCH, PUT, or POST, and if client is browser or web service. Can be much shorter if the Stale directive is implemented. This would allow a user to use new nonce without prompting user again for their username and password.

    # File lib/action_controller/metal/http_authentication.rb, line 311
    def validate_nonce(secret_key, request, value, seconds_to_timeout=5*60)
      return false if value.nil?
      t = ::Base64.decode64(value).split(":").first.to_i
      nonce(secret_key, t) == value && (t - Time.now.to_i).abs <= seconds_to_timeout
    end