diff --git a/CHANGELOG.md b/CHANGELOG.md
index 983626a..2845665 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ project adheres to [Semantic Versioning](https://semver.org/)
 
 ### Changed
 
+* Breaking change: Support OmniAuth 2 (#82).
 * Potential breaking change: case of `Omniauth::Cas::VERSION` module (#76).
 
 ### Removed
diff --git a/README.md b/README.md
index c347cb9..4e130f4 100644
--- a/README.md
+++ b/README.md
@@ -6,7 +6,7 @@
 [github_actions_status]: https://github.com/dlindahl/omniauth-cas/actions/workflows/ci.yml/badge.svg
 [releases]: https://github.com/dlindahl/omniauth-cas/releases
 
-This is a [OmniAuth][omniauth] 1.9 compatible port of the previously available
+This is a [OmniAuth][omniauth] 2.1+ compatible port of the previously available
 [OmniAuth CAS strategy][old_omniauth_cas] that was bundled with OmniAuth 0.3.
 
 * [View the documentation][document_up]
diff --git a/omniauth-cas.gemspec b/omniauth-cas.gemspec
index 45e7b60..699b671 100644
--- a/omniauth-cas.gemspec
+++ b/omniauth-cas.gemspec
@@ -28,5 +28,5 @@ Gem::Specification.new do |gem|
 
   gem.add_dependency 'addressable', '~> 2.8'
   gem.add_dependency 'nokogiri',    '~> 1.12'
-  gem.add_dependency 'omniauth',    '~> 1.9'
+  gem.add_dependency 'omniauth',    '~> 2.1'
 end
diff --git a/spec/omniauth/strategies/cas_spec.rb b/spec/omniauth/strategies/cas_spec.rb
index 6a272b7..0f734c2 100644
--- a/spec/omniauth/strategies/cas_spec.rb
+++ b/spec/omniauth/strategies/cas_spec.rb
@@ -38,7 +38,7 @@
 
     let(:redirect_params) { "service=#{Rack::Utils.escape("http://example.org/auth/cas/callback?url=#{Rack::Utils.escape(return_url)}")}" }
 
-    before { get url, nil, request_env }
+    before { post url, nil, request_env }
 
     it { is_expected.to be_redirect }
 
@@ -95,7 +95,7 @@
     it { is_expected.to include('ssl' => true) }
   end
 
-  describe 'GET /auth/cas' do
+  describe 'POST /auth/cas' do
     let(:return_url) { 'http://example.org/admin/foo' }
 
     context 'with a referer' do
@@ -115,7 +115,7 @@
     end
   end
 
-  describe 'GET /auth/cas/callback' do
+  describe 'POST /auth/cas/callback' do
     context 'without a ticket' do
       subject { last_response }
 
@@ -253,9 +253,7 @@
         it_behaves_like 'successful validation'
       end
     end
-  end
 
-  describe 'POST /auth/cas/callback' do
     describe 'with a Single Sign-Out logoutRequest' do
       subject do
         post 'auth/cas/callback', logoutRequest: logoutRequest
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index c7d891b..af9385c 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -13,6 +13,7 @@
 require 'webmock/rspec'
 
 OmniAuth.config.logger = Logger.new('/dev/null')
+OmniAuth.config.request_validation_phase = nil
 
 # This file was generated by the `rspec --init` command. Conventionally, all
 # specs live under a `spec` directory, which RSpec adds to the `$LOAD_PATH`.