Mitigate BREACH attack
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@ -1,4 +1,6 @@
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require 'rack/protection'
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require 'securerandom'
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require 'base64'
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module Rack
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module Protection
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@ -18,17 +20,112 @@ module Rack
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#
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class AuthenticityToken < Base
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default_options :authenticity_param => 'authenticity_token',
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:authenticity_token_length => 32,
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:allow_if => nil
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class << self
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def token(session)
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mask_token(session[:csrf])
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end
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def random_token(length = 32)
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SecureRandom.base64(length)
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end
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# Creates a masked version of the authenticity token that varies
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# on each request. The masking is used to mitigate SSL attacks
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# like BREACH.
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def mask_token(token)
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token = decode_token(token)
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one_time_pad = SecureRandom.random_bytes(token.length)
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encrypted_token = xor_byte_strings(one_time_pad, token)
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masked_token = one_time_pad + encrypted_token
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encode_token masked_token
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end
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# Essentially the inverse of +mask_token+.
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def unmask_decoded_token(masked_token)
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# Split the token into the one-time pad and the encrypted
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# value and decrypt it
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token_length = masked_token.length / 2
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one_time_pad = masked_token[0...token_length]
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encrypted_token = masked_token[token_length..-1]
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xor_byte_strings(one_time_pad, encrypted_token)
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end
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def encode_token(token)
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Base64.strict_encode64(token)
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end
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def decode_token(token)
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Base64.strict_decode64(token)
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end
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private
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def xor_byte_strings(s1, s2)
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s1.bytes.zip(s2.bytes).map { |(c1,c2)| c1 ^ c2 }.pack('c*')
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end
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end
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def accepts?(env)
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session = session env
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token = session[:csrf] ||= session['_csrf_token'] || random_string
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session[:csrf] ||= self.class.random_token(token_length)
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safe?(env) ||
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secure_compare(env['HTTP_X_CSRF_TOKEN'], token) ||
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secure_compare(Request.new(env).params[options[:authenticity_param]], token) ||
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valid_token?(session, env['HTTP_X_CSRF_TOKEN']) ||
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valid_token?(session, Request.new(env).params[options[:authenticity_param]]) ||
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( options[:allow_if] && options[:allow_if].call(env) )
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end
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private
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def token_length
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options[:authenticity_token_length]
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end
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# Checks the client's masked token to see if it matches the
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# session token.
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def valid_token?(session, token)
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return false if token.nil? || token.empty?
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begin
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token = self.class.decode_token(token)
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rescue ArgumentError # encoded_masked_token is invalid Base64
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return false
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end
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# See if it's actually a masked token or not. We should be able
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# to handle any unmasked tokens that we've issued without error.
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if unmasked_token?(token)
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compare_with_real_token token, session
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elsif masked_token?(token)
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token = self.class.unmask_decoded_token(token)
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compare_with_real_token token, session
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else
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false # Token is malformed
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end
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end
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def unmasked_token?(token)
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token.length == token_length
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end
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def masked_token?(token)
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token.length == token_length * 2
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end
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def compare_with_real_token(token, session)
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secure_compare(token, real_token(session))
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end
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def real_token(session)
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self.class.decode_token(session[:csrf])
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end
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end
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end
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end
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@ -1,4 +1,8 @@
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describe Rack::Protection::AuthenticityToken do
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let(:token) { described_class.random_token }
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let(:bad_token) { described_class.random_token }
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let(:session) { {:csrf => token} }
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it_behaves_like "any rack application"
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it "denies post requests without any token" do
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@ -6,22 +10,32 @@ describe Rack::Protection::AuthenticityToken do
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end
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it "accepts post requests with correct X-CSRF-Token header" do
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post('/', {}, 'rack.session' => {:csrf => "a"}, 'HTTP_X_CSRF_TOKEN' => "a")
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post('/', {}, 'rack.session' => session, 'HTTP_X_CSRF_TOKEN' => token)
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expect(last_response).to be_ok
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end
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it "accepts post requests with masked X-CSRF-Token header" do
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post('/', {}, 'rack.session' => session, 'HTTP_X_CSRF_TOKEN' => Rack::Protection::AuthenticityToken.token(session))
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expect(last_response).to be_ok
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end
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it "denies post requests with wrong X-CSRF-Token header" do
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post('/', {}, 'rack.session' => {:csrf => "a"}, 'HTTP_X_CSRF_TOKEN' => "b")
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post('/', {}, 'rack.session' => session, 'HTTP_X_CSRF_TOKEN' => bad_token)
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expect(last_response).not_to be_ok
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end
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it "accepts post form requests with correct authenticity_token field" do
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post('/', {"authenticity_token" => "a"}, 'rack.session' => {:csrf => "a"})
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post('/', {"authenticity_token" => token}, 'rack.session' => session)
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expect(last_response).to be_ok
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end
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it "accepts post form requests with masked authenticity_token field" do
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post('/', {"authenticity_token" => Rack::Protection::AuthenticityToken.token(session)}, 'rack.session' => session)
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expect(last_response).to be_ok
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end
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it "denies post form requests with wrong authenticity_token field" do
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post('/', {"authenticity_token" => "a"}, 'rack.session' => {:csrf => "b"})
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post('/', {"authenticity_token" => bad_token}, 'rack.session' => session)
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expect(last_response).not_to be_ok
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end
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@ -35,7 +49,7 @@ describe Rack::Protection::AuthenticityToken do
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run proc { |e| [200, {'Content-Type' => 'text/plain'}, ['hi']] }
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end
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post('/', {"csrf_param" => "a"}, 'rack.session' => {:csrf => "a"})
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post('/', {"csrf_param" => token}, 'rack.session' => {:csrf => token})
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expect(last_response).to be_ok
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end
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@ -43,4 +57,31 @@ describe Rack::Protection::AuthenticityToken do
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get('/', {}, {})
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expect(env['rack.session'][:csrf]).not_to be_nil
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end
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describe ".random_token" do
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it "outputs a base64 encoded 32 character string by default" do
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expect(Base64.strict_decode64(token).length).to eq(32)
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end
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it "outputs a base64 encoded string of the specified length" do
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token = described_class.random_token(64)
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expect(Base64.strict_decode64(token).length).to eq(64)
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end
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end
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describe ".mask_token" do
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it "generates unique masked values for a token" do
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first_masked_token = described_class.mask_token(token)
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second_masked_token = described_class.mask_token(token)
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expect(first_masked_token).not_to eq(second_masked_token)
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end
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end
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describe ".unmask_decoded_token" do
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it "unmasks a token to its original decoded value" do
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masked_token = described_class.decode_token(described_class.mask_token(token))
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unmasked_token = described_class.unmask_decoded_token(masked_token)
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expect(unmasked_token).to eq(described_class.decode_token(token))
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end
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end
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end
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describe Rack::Protection::FormToken do
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let(:token) { described_class.random_token }
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let(:bad_token) { described_class.random_token }
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let(:session) { {:csrf => token} }
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it_behaves_like "any rack application"
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it "denies post requests without any token" do
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@ -6,22 +10,32 @@ describe Rack::Protection::FormToken do
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end
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it "accepts post requests with correct X-CSRF-Token header" do
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post('/', {}, 'rack.session' => {:csrf => "a"}, 'HTTP_X_CSRF_TOKEN' => "a")
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post('/', {}, 'rack.session' => session, 'HTTP_X_CSRF_TOKEN' => token)
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expect(last_response).to be_ok
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end
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it "accepts post requests with masked X-CSRF-Token header" do
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post('/', {}, 'rack.session' => session, 'HTTP_X_CSRF_TOKEN' => Rack::Protection::FormToken.token(session))
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expect(last_response).to be_ok
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end
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it "denies post requests with wrong X-CSRF-Token header" do
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post('/', {}, 'rack.session' => {:csrf => "a"}, 'HTTP_X_CSRF_TOKEN' => "b")
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post('/', {}, 'rack.session' => session, 'HTTP_X_CSRF_TOKEN' => bad_token)
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expect(last_response).not_to be_ok
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end
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it "accepts post form requests with correct authenticity_token field" do
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post('/', {"authenticity_token" => "a"}, 'rack.session' => {:csrf => "a"})
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post('/', {"authenticity_token" => token}, 'rack.session' => session)
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expect(last_response).to be_ok
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end
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it "accepts post form requests with masked authenticity_token field" do
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post('/', {"authenticity_token" => Rack::Protection::FormToken.token(session)}, 'rack.session' => session)
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expect(last_response).to be_ok
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end
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it "denies post form requests with wrong authenticity_token field" do
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post('/', {"authenticity_token" => "a"}, 'rack.session' => {:csrf => "b"})
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post('/', {"authenticity_token" => bad_token}, 'rack.session' => session)
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expect(last_response).not_to be_ok
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end
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describe Rack::Protection::RemoteToken do
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let(:token) { described_class.random_token }
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let(:bad_token) { described_class.random_token }
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let(:session) { {:csrf => token} }
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it_behaves_like "any rack application"
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it "accepts post requests with no referrer" do
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@ -16,25 +20,37 @@ describe Rack::Protection::RemoteToken do
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it "accepts post requests with a remote referrer and correct X-CSRF-Token header" do
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post('/', {}, 'HTTP_REFERER' => 'http://example.com/foo', 'HTTP_HOST' => 'example.org',
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'rack.session' => {:csrf => "a"}, 'HTTP_X_CSRF_TOKEN' => "a")
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'rack.session' => session, 'HTTP_X_CSRF_TOKEN' => token)
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expect(last_response).to be_ok
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end
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it "accepts post requests with a remote referrer and masked X-CSRF-Token header" do
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post('/', {}, 'HTTP_REFERER' => 'http://example.com/foo', 'HTTP_HOST' => 'example.org',
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'rack.session' => session, 'HTTP_X_CSRF_TOKEN' => Rack::Protection::RemoteToken.token(session))
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expect(last_response).to be_ok
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end
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it "denies post requests with a remote referrer and wrong X-CSRF-Token header" do
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post('/', {}, 'HTTP_REFERER' => 'http://example.com/foo', 'HTTP_HOST' => 'example.org',
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'rack.session' => {:csrf => "a"}, 'HTTP_X_CSRF_TOKEN' => "b")
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'rack.session' => session, 'HTTP_X_CSRF_TOKEN' => bad_token)
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expect(last_response).not_to be_ok
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end
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it "accepts post form requests with a remote referrer and correct authenticity_token field" do
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post('/', {"authenticity_token" => "a"}, 'HTTP_REFERER' => 'http://example.com/foo',
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'HTTP_HOST' => 'example.org', 'rack.session' => {:csrf => "a"})
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post('/', {"authenticity_token" => token}, 'HTTP_REFERER' => 'http://example.com/foo',
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'HTTP_HOST' => 'example.org', 'rack.session' => session)
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expect(last_response).to be_ok
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end
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it "accepts post form requests with a remote referrer and masked authenticity_token field" do
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post('/', {"authenticity_token" => Rack::Protection::RemoteToken.token(session)}, 'HTTP_REFERER' => 'http://example.com/foo',
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'HTTP_HOST' => 'example.org', 'rack.session' => session)
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expect(last_response).to be_ok
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end
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it "denies post form requests with a remote referrer and wrong authenticity_token field" do
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post('/', {"authenticity_token" => "a"}, 'HTTP_REFERER' => 'http://example.com/foo',
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'HTTP_HOST' => 'example.org', 'rack.session' => {:csrf => "b"})
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post('/', {"authenticity_token" => bad_token}, 'HTTP_REFERER' => 'http://example.com/foo',
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'HTTP_HOST' => 'example.org', 'rack.session' => session)
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expect(last_response).not_to be_ok
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end
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end
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