diff --git a/CHANGELOG.md b/CHANGELOG.md
index a1bbb24d..78627b86 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## master
 
+**Bug fixes**:
+
+- [#168](https://github.com/castle/castle-ruby/pull/168) do not apply whitelisting by default
+
 ## 3.6.0 (2020-01-07)
 
 **BREAKING CHANGES:**
diff --git a/README.md b/README.md
index dd6ac95b..38b58bde 100644
--- a/README.md
+++ b/README.md
@@ -67,15 +67,24 @@ Castle.configure do |config|
 
   # Whitelisted and Blacklisted headers are case insensitive and allow to use _ and - as a separator, http prefixes are removed
   # Whitelisted headers
-  # @note In case of the whitelist, we won't send the values of other headers but we will send their names
-  config.whitelisted = ['X_HEADER']
-  # or append to default
-  config.whitelisted += ['http-x-header']
-
-  # Blacklisted headers take advantage over whitelisted elements
+  # By default, the SDK sends all HTTP headers, except for Cookie and Authorization.
+  # If you decide to use a whitelist, the SDK will:
+  # - always send the User-Agent header
+  # - send scrubbed values of non-whitelisted headers
+  # - send proper values of whitelisted headers.
+  # @example
+  #   config.whitelisted = ['X_HEADER']
+  #   # will send { 'User-Agent' => 'Chrome', 'X_HEADER' => 'proper value', 'Any-Other-Header' => true }
+  #
+  # We highly suggest using blacklist instead of whitelist, so that Castle can use as many data points
+  # as possible to secure your users. If you want to use the whitelist, this is the minimal
+  # amount of headers we recommend:
+  config.whitelisted = Castle::Configuration::DEFAULT_WHITELIST
+
+  # Blacklisted headers take precedence over whitelisted elements
+  # We always blacklist Cookie and Authentication headers. If you use any other headers that
+  # might contain sensitive information, you should blacklist them.
   config.blacklisted = ['HTTP-X-header']
-  # or append to default
-  config.blacklisted += ['X_HEADER']
 end
 ```
 
diff --git a/lib/castle/configuration.rb b/lib/castle/configuration.rb
index ab45118f..012104ec 100644
--- a/lib/castle/configuration.rb
+++ b/lib/castle/configuration.rb
@@ -9,22 +9,27 @@ class Configuration
     FAILOVER_STRATEGY = :allow
     REQUEST_TIMEOUT = 500 # in milliseconds
     FAILOVER_STRATEGIES = %i[allow deny challenge throw].freeze
-    WHITELISTED = [
-      'User-Agent',
-      'Accept-Language',
-      'Accept-Encoding',
-      'Accept-Charset',
-      'Accept',
-      'Accept-Datetime',
-      'X-Forwarded-For',
-      'Forwarded',
-      'X-Forwarded',
-      'X-Real-IP',
-      'REMOTE_ADDR',
-      'X-Forwarded-For',
-      'CF_CONNECTING_IP'
+
+    # @note this value is not assigned as we don't recommend using a whitelist. If you need to use
+    #   one, this constant is provided as a good default.
+    DEFAULT_WHITELIST = %w[
+      Accept
+      Accept-Charset
+      Accept-Datetime
+      Accept-Encoding
+      Accept-Language
+      Cache-Control
+      Connection
+      Content-Length
+      Content-Type
+      Host
+      Origin
+      Pragma
+      Referer
+      TE
+      Upgrade-Insecure-Requests
+      X-Castle-Client-Id
     ].freeze
-    BLACKLISTED = ['HTTP_COOKIE'].freeze
 
     attr_accessor :host, :port, :request_timeout, :url_prefix
     attr_reader :api_secret, :whitelisted, :blacklisted, :failover_strategy
@@ -36,8 +41,8 @@ def initialize
       self.host = HOST
       self.port = PORT
       self.url_prefix = URL_PREFIX
-      self.whitelisted = WHITELISTED
-      self.blacklisted = BLACKLISTED
+      self.whitelisted = [].freeze
+      self.blacklisted = [].freeze
       self.api_secret = ''
     end
 
diff --git a/lib/castle/extractors/headers.rb b/lib/castle/extractors/headers.rb
index 84017134..edfb0810 100644
--- a/lib/castle/extractors/headers.rb
+++ b/lib/castle/extractors/headers.rb
@@ -4,23 +4,45 @@ module Castle
   module Extractors
     # used for extraction of cookies and headers from the request
     class Headers
+      # Headers that we will never scrub, even if they land on the configuration blacklist.
+      ALWAYS_INCLUDED_HEADERS = %w[User-Agent].freeze
+
+      # Headers that will always be scrubbed, even if whitelisted.
+      ALWAYS_SCRUBBED_HEADERS = %w[Cookie Authorization].freeze
+
+      # Rack does not add the HTTP_ prefix to Content-Length for some reason
+      CONTENT_LENGTH = 'CONTENT_LENGTH'
+
+      # Prefix that Rack adds for HTTP headers
+      HTTP_HEADER_PREFIX = 'HTTP_'
+
+      private_constant :ALWAYS_INCLUDED_HEADERS, :ALWAYS_SCRUBBED_HEADERS,
+                       :CONTENT_LENGTH, :HTTP_HEADER_PREFIX
+
+      # @param request [Rack::Request]
       def initialize(request)
-        @request = request
-        @request_env = @request.env
+        @request_env = request.env
         @formatter = HeaderFormatter.new
       end
 
       # Serialize HTTP headers
+      # @return [Hash]
       def call
-        @request_env.keys.each_with_object({}) do |header, acc|
-          name = @formatter.call(header)
+        @request_env.keys.each_with_object({}) do |env_header, acc|
+          next unless env_header.start_with?(HTTP_HEADER_PREFIX) || env_header == CONTENT_LENGTH
+
+          header = @formatter.call(env_header)
 
-          if Castle.config.whitelisted.include?(name) && !Castle.config.blacklisted.include?(name)
-            acc[name] = @request_env[header]
+          if ALWAYS_SCRUBBED_HEADERS.include?(header)
+            acc[header] = true
+          elsif ALWAYS_INCLUDED_HEADERS.include?(header)
+            acc[header] = @request_env[env_header]
+          elsif Castle.config.blacklisted.include?(header)
+            acc[header] = true
+          elsif Castle.config.whitelisted.empty? || Castle.config.whitelisted.include?(header)
+            acc[header] = @request_env[env_header]
           else
-            # When a header is not whitelisted or blacklisted, we're not suppose to send
-            # it's value but we should send it's name to indicate it's presence
-            acc[name] = true
+            acc[header] = true
           end
         end
       end
diff --git a/spec/lib/castle/client_spec.rb b/spec/lib/castle/client_spec.rb
index d362c123..393fc1d4 100644
--- a/spec/lib/castle/client_spec.rb
+++ b/spec/lib/castle/client_spec.rb
@@ -22,13 +22,7 @@
 
   let(:headers) do
     {
-      'Rack.version': true, 'Rack.input': true, 'Rack.errors': true,
-      'Rack.multithread': true, 'Rack.multiprocess': true, 'Rack.run-Once': true,
-      'Request-Method': true, 'Server-Name': true, 'Server-Port': true,
-      'Query-String': true, 'Path-Info': true, 'Rack.url-Scheme': true,
-      'Https': true, 'Script-Name': true, 'Content-Length': true,
-      'User-Agent': ua, 'X-Forwarded-For': ip.to_s, 'Rack.request.cookie-Hash': true,
-      'Rack.request.cookie-String': true, 'Cookie': true
+      'Content-Length': '0', 'User-Agent': ua, 'X-Forwarded-For': ip.to_s, 'Cookie': true
     }
   end
   let(:context) do
diff --git a/spec/lib/castle/configuration_spec.rb b/spec/lib/castle/configuration_spec.rb
index a625c7e6..db9a2ab3 100644
--- a/spec/lib/castle/configuration_spec.rb
+++ b/spec/lib/castle/configuration_spec.rb
@@ -77,7 +77,7 @@
 
   describe 'whitelisted' do
     it do
-      expect(config.whitelisted.size).to be_eql(13)
+      expect(config.whitelisted.size).to be_eql(0)
     end
 
     context 'with setter' do
@@ -88,19 +88,11 @@
         expect(config.whitelisted).to be_eql(['Header'])
       end
     end
-
-    context 'when appending' do
-      before do
-        config.whitelisted += ['header']
-      end
-      it { expect(config.whitelisted).to be_include('Header') }
-      it { expect(config.whitelisted.size).to be_eql(14) }
-    end
   end
 
   describe 'blacklisted' do
     it do
-      expect(config.blacklisted.size).to be_eql(1)
+      expect(config.blacklisted.size).to be_eql(0)
     end
 
     context 'with setter' do
@@ -111,14 +103,6 @@
         expect(config.blacklisted).to be_eql(['Header'])
       end
     end
-
-    context 'when appending' do
-      before do
-        config.blacklisted += ['header']
-      end
-      it { expect(config.blacklisted).to be_include('Header') }
-      it { expect(config.blacklisted.size).to be_eql(2) }
-    end
   end
 
   describe 'failover_strategy' do
diff --git a/spec/lib/castle/context/default_spec.rb b/spec/lib/castle/context/default_spec.rb
index cfe090dd..fd183a09 100644
--- a/spec/lib/castle/context/default_spec.rb
+++ b/spec/lib/castle/context/default_spec.rb
@@ -9,8 +9,8 @@
   let(:env) do
     Rack::MockRequest.env_for('/',
                               'HTTP_X_FORWARDED_FOR' => ip,
-                              'HTTP-Accept-Language' => 'en',
-                              'HTTP-User-Agent' => 'test',
+                              'HTTP_ACCEPT_LANGUAGE' => 'en',
+                              'HTTP_USER_AGENT' => 'test',
                               'HTTP_COOKIE' => "__cid=#{cookie_id};other=efgh")
   end
   let(:request) { Rack::Request.new(env) }
@@ -23,18 +23,17 @@
 
   it { expect(default_context[:active]).to be_eql(true) }
   it { expect(default_context[:origin]).to be_eql('web') }
-  it {
+
+  it do
     expect(default_context[:headers]).to be_eql(
-      'Rack.version' => true, 'Rack.input' => true, 'Rack.errors' => true,
-      'Rack.multithread' => true, 'Rack.multiprocess' => true, 'Rack.run-Once' => true,
-      'Request-Method' => true, 'Server-Name' => true, 'Server-Port' => true,
-      'Query-String' => true, 'Path-Info' => true, 'Rack.url-Scheme' => true,
-      'Https' => true, 'Script-Name' => true, 'Content-Length' => true,
-      'X-Forwarded-For' => '1.2.3.4', 'Accept-Language' => 'en', 'User-Agent' => 'test',
-      'Rack.request.cookie-Hash' => true, 'Rack.request.cookie-String' => true,
+      'X-Forwarded-For' => '1.2.3.4',
+      'Accept-Language' => 'en',
+      'User-Agent' => 'test',
+      'Content-Length' => '0',
       'Cookie' => true
     )
-  }
+  end
+
   it { expect(default_context[:ip]).to be_eql(ip) }
   it { expect(default_context[:library][:name]).to be_eql('castle-rb') }
   it { expect(default_context[:library][:version]).to be_eql(version) }
diff --git a/spec/lib/castle/extractors/headers_spec.rb b/spec/lib/castle/extractors/headers_spec.rb
index bf97f15c..c67adeb6 100644
--- a/spec/lib/castle/extractors/headers_spec.rb
+++ b/spec/lib/castle/extractors/headers_spec.rb
@@ -1,32 +1,88 @@
 # frozen_string_literal: true
 
 describe Castle::Extractors::Headers do
-  subject(:extractor) { described_class.new(request) }
+  subject(:headers) { described_class.new(request).call }
 
   let(:client_id) { 'abcd' }
   let(:env) do
-    Rack::MockRequest.env_for('/',
-                              'HTTP_X_FORWARDED_FOR' => '1.2.3.4',
-                              'HTTP_OK' => 'OK',
-                              'TEST' => '1',
-                              'HTTP_COOKIE' => "__cid=#{client_id};other=efgh")
+    Rack::MockRequest.env_for(
+      '/',
+      'Action-Dispatch.request.content-Type' => 'application/json',
+      'HTTP_AUTHORIZATION' => 'Basic 123456',
+      'HTTP_COOKIE' => "__cid=#{client_id};other=efgh",
+      'HTTP_OK' => 'OK',
+      'HTTP_ACCEPT' => 'application/json',
+      'HTTP_X_FORWARDED_FOR' => '1.2.3.4',
+      'HTTP_USER_AGENT' => 'Mozilla 1234',
+      'TEST' => '1'
+    )
   end
   let(:request) { Rack::Request.new(env) }
 
-  describe 'extract http headers with whitelisted and blacklisted support' do
+  context 'when whitelist is not set in the configuration' do
+    it do
+      is_expected.to eq('Accept' => 'application/json',
+                        'Authorization' => true,
+                        'Cookie' => true,
+                        'Content-Length' => '0',
+                        'Ok' => 'OK',
+                        'User-Agent' => 'Mozilla 1234',
+                        'X-Forwarded-For' => '1.2.3.4')
+    end
+  end
+
+  context 'when whitelist is set in the configuration' do
+    before { Castle.config.whitelisted = %w[Accept OK] }
+
+    it do
+      is_expected.to eq('Accept' => 'application/json',
+                        'Authorization' => true,
+                        'Cookie' => true,
+                        'Content-Length' => true,
+                        'Ok' => 'OK',
+                        'User-Agent' => 'Mozilla 1234',
+                        'X-Forwarded-For' => true)
+    end
+  end
+
+  context 'when blacklist is set in the configuration' do
+    context 'with a User-Agent' do
+      before { Castle.config.blacklisted = %w[User-Agent] }
+
+      it do
+        is_expected.to eq('Accept' => 'application/json',
+                          'Authorization' => true,
+                          'Cookie' => true,
+                          'Content-Length' => '0',
+                          'Ok' => 'OK',
+                          'User-Agent' => 'Mozilla 1234',
+                          'X-Forwarded-For' => '1.2.3.4')
+      end
+    end
+
+    context 'with a different header' do
+      before { Castle.config.blacklisted = %w[Accept] }
+
+      it do
+        is_expected.to eq('Accept' => true,
+                          'Authorization' => true,
+                          'Cookie' => true,
+                          'Content-Length' => '0',
+                          'Ok' => 'OK',
+                          'User-Agent' => 'Mozilla 1234',
+                          'X-Forwarded-For' => '1.2.3.4')
+      end
+    end
+  end
+
+  context 'when a header is both whitelisted and blacklisted' do
     before do
-      Castle.config.whitelisted += ['TEST']
+      Castle.config.whitelisted = %w[Accept]
+      Castle.config.blacklisted = %w[Accept]
     end
+
     it do
-      expect(extractor.call).to eql(
-        'Test' => '1', 'Ok' => true, 'Rack.version' => true,
-        'Rack.input' => true, 'Rack.errors' => true, 'Rack.multithread' => true,
-        'Rack.multiprocess' => true, 'Rack.run-Once' => true, 'Request-Method' => true,
-        'Server-Name' => true, 'Server-Port' => true, 'Query-String' => true,
-        'Path-Info' => true, 'Rack.url-Scheme' => true, 'Https' => true,
-        'Script-Name' => true, 'Content-Length' => true, 'X-Forwarded-For' => '1.2.3.4',
-        'Cookie' => true
-      )
+      expect(headers['Accept']).to eq(true)
     end
   end
 end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index a539a209..cc2d71b8 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -12,11 +12,14 @@
 
 require 'castle'
 
-Castle.configure do |config|
-  config.api_secret = 'secret'
-end
-
 WebMock.disable_net_connect!(allow_localhost: true)
 
 RSpec.configure do |config|
+  config.before do
+    Castle.instance_variable_set(:@configuration, Castle::Configuration.new)
+
+    Castle.configure do |cfg|
+      cfg.api_secret = 'secret'
+    end
+  end
 end