diff --git a/.travis.yml b/.travis.yml
index b3a9e20..3d063ed 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,9 @@
 bundler_args: --without development
 before_install:
-  - gem update --system
-  - gem update bundler
+  - gem uninstall -v '>= 2' -i $(rvm gemdir)@global -ax bundler || true
+  - gem install bundler -v '1.17.3'
+install:
+ - bundle _1.17.3_ install --jobs=3 --retry=3
 cache: bundler
 env:
   global:
diff --git a/Gemfile b/Gemfile
index edb91a9..e92c9a7 100644
--- a/Gemfile
+++ b/Gemfile
@@ -13,14 +13,14 @@ end
 
 group :test do
   gem 'coveralls', :require => false
-  gem 'hashie', '>= 3.4.6', '< 3.7.0', :platforms => [:jruby_18]
+  gem 'hashie', '>= 3.4.6', '~> 4.0.0', :platforms => [:jruby_18]
   gem 'json', '~> 2.0.3', :platforms => %i[jruby_18 jruby_19 ruby_19]
   gem 'mime-types', '~> 3.1', :platforms => [:jruby_18]
   gem 'rack', '>= 2.0.6', :platforms => %i[jruby_18 jruby_19 ruby_19 ruby_20 ruby_21]
   gem 'rack-test'
   gem 'rest-client', '~> 2.0.0', :platforms => [:jruby_18]
   gem 'rspec', '~> 3.5.0'
-  gem 'rubocop', '>= 0.58.2', :platforms => %i[ruby_20 ruby_21 ruby_22 ruby_23 ruby_24]
+  gem 'rubocop', '>= 0.58.2', '< 0.69.0', :platforms => %i[ruby_20 ruby_21 ruby_22 ruby_23 ruby_24]
   gem 'tins', '~> 1.13.0', :platforms => %i[jruby_18 jruby_19 ruby_19]
 end
 
diff --git a/lib/omniauth.rb b/lib/omniauth.rb
index c53ee25..dc315ee 100644
--- a/lib/omniauth.rb
+++ b/lib/omniauth.rb
@@ -132,7 +132,7 @@ module OmniAuth
   end
 
   module Utils
-  module_function
+  module_function # rubocop:disable Layout/IndentationWidth
 
     def form_css
       "<style type='text/css'>#{OmniAuth.config.form_css}</style>"
diff --git a/lib/omniauth/builder.rb b/lib/omniauth/builder.rb
index a513571..717b4be 100644
--- a/lib/omniauth/builder.rb
+++ b/lib/omniauth/builder.rb
@@ -1,24 +1,5 @@
 module OmniAuth
   class Builder < ::Rack::Builder
-    def initialize(app, &block)
-      @options = nil
-      if rack14? || rack2?
-        super
-      else
-        @app = app
-        super(&block)
-        @ins << @app
-      end
-    end
-
-    def rack14?
-      Rack.release.start_with?('1.') && (Rack.release.split('.')[1].to_i >= 4)
-    end
-
-    def rack2?
-      Rack.release.start_with? '2.'
-    end
-
     def on_failure(&block)
       OmniAuth.config.on_failure = block
     end
@@ -40,7 +21,7 @@ module OmniAuth
     end
 
     def options(options = false)
-      return @options || {} if options == false
+      return @options ||= {} if options == false
 
       @options = options
     end
diff --git a/omniauth.gemspec b/omniauth.gemspec
index aab676d..cf0f624 100644
--- a/omniauth.gemspec
+++ b/omniauth.gemspec
@@ -5,7 +5,7 @@ $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 require 'omniauth/version'
 
 Gem::Specification.new do |spec|
-  spec.add_dependency 'hashie', ['>= 3.4.6', '< 3.7.0']
+  spec.add_dependency 'hashie', ['>= 3.4.6', '~> 4.0.0']
   spec.add_dependency 'rack', ['>= 1.6.2', '< 3']
   spec.add_development_dependency 'bundler', '~> 1.14'
   spec.add_development_dependency 'rake', '~> 12.0'
diff --git a/spec/omniauth/builder_spec.rb b/spec/omniauth/builder_spec.rb
index 92d13fb..4e04e38 100644
--- a/spec/omniauth/builder_spec.rb
+++ b/spec/omniauth/builder_spec.rb
@@ -47,4 +47,84 @@ describe OmniAuth::Builder do
       b.provider k
     end
   end
+
+  describe '#on_failure' do
+    it 'passes the block to the config' do
+      prok = proc {}
+
+      with_config_reset(:on_failure) do
+        OmniAuth::Builder.new(nil).on_failure(&prok)
+
+        expect(OmniAuth.config.on_failure).to eq(prok)
+      end
+    end
+  end
+
+  describe '#before_options_phase' do
+    it 'passes the block to the config' do
+      prok = proc {}
+
+      with_config_reset(:before_options_phase) do
+        OmniAuth::Builder.new(nil).before_options_phase(&prok)
+
+        expect(OmniAuth.config.before_options_phase).to eq(prok)
+      end
+    end
+  end
+
+  describe '#before_request_phase' do
+    it 'passes the block to the config' do
+      prok = proc {}
+
+      with_config_reset(:before_request_phase) do
+        OmniAuth::Builder.new(nil).before_request_phase(&prok)
+
+        expect(OmniAuth.config.before_request_phase).to eq(prok)
+      end
+    end
+  end
+
+  describe '#before_callback_phase' do
+    it 'passes the block to the config' do
+      prok = proc {}
+
+      with_config_reset(:before_callback_phase) do
+        OmniAuth::Builder.new(nil).before_callback_phase(&prok)
+
+        expect(OmniAuth.config.before_callback_phase).to eq(prok)
+      end
+    end
+  end
+
+  describe '#configure' do
+    it 'passes the block to the config' do
+      prok = proc {}
+      allow(OmniAuth).to receive(:configure).and_call_original
+
+      OmniAuth::Builder.new(nil).configure(&prok)
+
+      expect(OmniAuth).to have_received(:configure) do |&block|
+        expect(block).to eq(prok)
+      end
+    end
+  end
+
+  describe '#call' do
+    it 'passes env to to_app.call' do
+      app = lambda { |_env| [200, {}, []] }
+      builder = OmniAuth::Builder.new(app)
+      env = {'REQUEST_METHOD' => 'GET', 'PATH_INFO' => '/some/path'}
+      allow(app).to receive(:call).and_call_original
+
+      builder.call(env)
+
+      expect(app).to have_received(:call).with(env)
+    end
+  end
+
+  def with_config_reset(option)
+    old_config = OmniAuth.config.send(option)
+    yield
+    OmniAuth.config.send("#{option}=", old_config)
+  end
 end