diff --git a/CHANGELOG.md b/CHANGELOG.md
index 12eff04..8b0e345 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,9 @@
+## 5.1.0 (2019-02-12)
+
+Changes:
+
+  - support for an access_token param, validated by facebook's debug token api
+  
 ## 5.0.0 (2018-03-29)
 
 Changes:
diff --git a/README.md b/README.md
index 09cf451..a246e84 100644
--- a/README.md
+++ b/README.md
@@ -136,6 +136,11 @@ When you call `/auth/facebook/callback` in the success callback of `FB.login` th
 2. extract the authorization code contained in it
 3. and hit Facebook and obtain an access token which will get placed in the `request.env['omniauth.auth']['credentials']` hash.
 
+## Client-side Flow with Facebook Android and ioS SDK
+
+A long lived access token is returned by the native sdks.  This flow is supported by sending an "access_token" query parameter to your callback.  This token is then verified with facebook using your client_id and client_secret before being used.
+Be sure to leave CSRF protection on for this method of authentication.
+
 ## Token Expiry
 
 The expiration time of the access token you obtain will depend on which flow you are using.
diff --git a/lib/omniauth/strategies/facebook.rb b/lib/omniauth/strategies/facebook.rb
index 12a9003..61a12d5 100644
--- a/lib/omniauth/strategies/facebook.rb
+++ b/lib/omniauth/strategies/facebook.rb
@@ -8,6 +8,8 @@ module OmniAuth
   module Strategies
     class Facebook < OmniAuth::Strategies::OAuth2
       class NoAuthorizationCodeError < StandardError; end
+      class MissingScopesError < StandardError; end
+      class AppIdMismatchError < StandardError; end
 
       DEFAULT_SCOPE = 'email'
 
@@ -63,9 +65,13 @@ def info_options
       end
 
       def callback_phase
-        with_authorization_code! do
+        with_authorization_parameter! do
           super
         end
+      rescue AppIdMismatchError => e
+        fail!(:app_id_mismatch, e)
+      rescue MissingScopesError => e
+        fail!(:missing_scopes, e)
       rescue NoAuthorizationCodeError => e
         fail!(:no_authorization_code, e)
       rescue OmniAuth::Facebook::SignedRequest::UnknownSignatureAlgorithmError => e
@@ -76,7 +82,7 @@ def callback_phase
       #      phase and it must match during the access_token phase:
       #      https://github.com/facebook/facebook-php-sdk/blob/master/src/base_facebook.php#L477
       def callback_url
-        if @authorization_code_from_signed_request_in_cookie
+        if defined?(@auth_code_from_cookie) && @auth_code_from_cookie
           ''
         else
           # Fixes regression in omniauth-oauth2 v1.4.0 by https://github.com/intridea/omniauth-oauth2/commit/85fdbe117c2a4400d001a6368cc359d88f40abc7
@@ -107,31 +113,47 @@ def authorize_params
       protected
 
       def build_access_token
-        super.tap do |token|
-          token.options.merge!(access_token_options)
+        if request.params["access_token"]
+          build_access_token_from_request(request.params["access_token"])
+        else
+          super.tap do |token|
+            token.options.merge!(access_token_options)
+          end
         end
       end
 
       private
 
-      def signed_request_from_cookie
-        @signed_request_from_cookie ||= raw_signed_request_from_cookie && OmniAuth::Facebook::SignedRequest.parse(raw_signed_request_from_cookie, client.secret)
+      def build_access_token_from_request(access_token_param)
+        token_hash = { :access_token => access_token_param }
+        access_token = ::OAuth2::AccessToken.from_hash(client, token_hash.update(access_token_options))
+        verify_access_token!(access_token)
+        return access_token
       end
 
-      def raw_signed_request_from_cookie
-        request.cookies["fbsr_#{client.id}"]
+      def verify_access_token!(access_token)
+        opts = { params: { input_token: access_token.token, access_token: app_access_token }}
+        token_info = access_token.get('/debug_token', opts)
+        missing_scopes = authorize_params.scope.split(',').collect(&:strip) - token_info.parsed.fetch("data", {}).fetch("scopes", [])
+        raise MissingScopesError, "Missing scopes #{missing_scopes.join(', ')}" if missing_scopes.any?
+      rescue ::OAuth2::Error => e
+        raise AppIdMismatchError, "Failed to validate token: #{e.message}"
+      end
+
+      def app_access_token
+        "%s|%s" % [client.id, client.secret]
       end
 
       # Picks the authorization code in order, from:
       #
       # 1. The request 'code' param (manual callback from standard server-side flow)
       # 2. A signed request from cookie (passed from the client during the client-side flow)
-      def with_authorization_code!
-        if request.params.key?('code')
+      def with_authorization_parameter!
+        if request.params.key?('code') || request.params.key?('access_token')
           yield
         elsif code_from_signed_request = signed_request_from_cookie && signed_request_from_cookie['code']
           request.params['code'] = code_from_signed_request
-          @authorization_code_from_signed_request_in_cookie = true
+          @auth_code_from_cookie = true
           # NOTE The code from the signed fbsr_XXX cookie is set by the FB JS SDK will confirm that the identity of the
           #      user contained in the signed request matches the user loading the app.
           original_provider_ignores_state = options.provider_ignores_state
@@ -140,14 +162,22 @@ def with_authorization_code!
             yield
           ensure
             request.params.delete('code')
-            @authorization_code_from_signed_request_in_cookie = false
+            @auth_code_from_cookie = false
             options.provider_ignores_state = original_provider_ignores_state
           end
         else
-          raise NoAuthorizationCodeError, 'must pass either a `code` (via URL or by an `fbsr_XXX` signed request cookie)'
+          raise NoAuthorizationCodeError, 'must pass either a `access_token` param or a `code` (via URL param or by an `fbsr_XXX` signed request cookie)'
         end
       end
 
+      def signed_request_from_cookie
+        @signed_request_from_cookie ||= raw_signed_request_from_cookie && OmniAuth::Facebook::SignedRequest.parse(raw_signed_request_from_cookie, client.secret)
+      end
+
+      def raw_signed_request_from_cookie
+        request.cookies["fbsr_#{client.id}"]
+      end
+
       def prune!(hash)
         hash.delete_if do |_, value|
           prune!(value) if value.is_a?(Hash)
diff --git a/test/helper.rb b/test/helper.rb
index bd1b82b..e7e62ba 100644
--- a/test/helper.rb
+++ b/test/helper.rb
@@ -32,7 +32,7 @@ class TestCase < Minitest::Test
 
 class StrategyTestCase < TestCase
   def setup
-    @request = stub('Request')
+    @request = stub('Request', {})
     @request.stubs(:params).returns({})
     @request.stubs(:cookies).returns({})
     @request.stubs(:env).returns({})
@@ -41,6 +41,8 @@ def setup
 
     @client_id = '123'
     @client_secret = '53cr3tz'
+
+    @options = nil
   end
 
   def strategy
diff --git a/test/strategy_test.rb b/test/strategy_test.rb
index 3cc4a9a..3954260 100644
--- a/test/strategy_test.rb
+++ b/test/strategy_test.rb
@@ -391,118 +391,152 @@ def setup
   end
 end
 
-module SignedRequestHelpers
-  def signed_request(payload, secret)
-    encoded_payload = base64_encode_url(MultiJson.encode(payload))
-    encoded_signature = base64_encode_url(signature(encoded_payload, secret))
-    [encoded_signature, encoded_payload].join('.')
-  end
-
-  def base64_encode_url(value)
-    Base64.encode64(value).tr('+/', '-_').gsub(/\n/, '')
-  end
-
-  def signature(payload, secret, algorithm = OpenSSL::Digest::SHA256.new)
-    OpenSSL::HMAC.digest(algorithm, secret, payload)
-  end
-end
-
-module SignedRequestTests
-  class TestCase < StrategyTestCase
-    include SignedRequestHelpers
-  end
-
-  class CookieAndParamNotPresentTest < TestCase
+module GettingAccessTokenTests
+  class CookieAndParamNotPresentTest < StrategyTestCase
     test 'is nil' do
       assert_nil strategy.send(:signed_request_from_cookie)
     end
 
     test 'throws an error on calling build_access_token' do
-      assert_raises(OmniAuth::Strategies::Facebook::NoAuthorizationCodeError) { strategy.send(:with_authorization_code!) {} }
-    end
-  end
-
-  class CookiePresentTest < TestCase
-    def setup(algo = nil)
-      super()
-      @payload = {
-        'algorithm' => algo || 'HMAC-SHA256',
-        'code' => 'm4c0d3z',
-        'issued_at' => Time.now.to_i,
-        'user_id' => '123456'
-      }
-
-      @request.stubs(:cookies).returns({"fbsr_#{@client_id}" => signed_request(@payload, @client_secret)})
-    end
-
-    test 'parses the access code out from the cookie' do
-      assert_equal @payload, strategy.send(:signed_request_from_cookie)
-    end
-
-    test 'throws an error if the algorithm is unknown' do
-      setup('UNKNOWN-ALGO')
-      assert_equal "unknown algorithm: UNKNOWN-ALGO", assert_raises(OmniAuth::Facebook::SignedRequest::UnknownSignatureAlgorithmError) { strategy.send(:signed_request_from_cookie) }.message
+      assert_raises(OmniAuth::Strategies::Facebook::NoAuthorizationCodeError) { strategy.send(:with_authorization_parameter!) {} }
     end
   end
 
-  class EmptySignedRequestTest < TestCase
-    def setup
-      super
-      @request.stubs(:params).returns({'signed_request' => ''})
-    end
-
-    test 'empty param' do
-      assert_equal nil, strategy.send(:signed_request_from_cookie)
+  class MissingParamsAndCookieRequestTest < StrategyTestCase
+    test 'calls fail! when a code or access_token is not included in the params' do
+      strategy.expects(:fail!).times(1).with(:no_authorization_code, kind_of(OmniAuth::Strategies::Facebook::NoAuthorizationCodeError))
+      strategy.callback_phase
     end
   end
 
-  class MissingCodeInParamsRequestTest < TestCase
+  class BadTokenTest < StrategyTestCase
     def setup
       super
-      @request.stubs(:params).returns({})
+      @access_token = stub('OAuth2::AccessToken')
+      @access_token.stubs(:token).returns('fake_token')
+      ::OAuth2::AccessToken.stubs(:from_hash).returns(@access_token)
+      @request.stubs(:params).returns({'access_token' => 'fake_token'})
+      strategy.stubs(:app_access_token).returns('other_token')
     end
 
-    test 'calls fail! when a code is not included in the params' do
-      strategy.expects(:fail!).times(1).with(:no_authorization_code, kind_of(OmniAuth::Strategies::Facebook::NoAuthorizationCodeError))
-      strategy.callback_phase
+    test 'throws error when access token bad' do
+      params = { params: { input_token: 'fake_token', access_token: 'other_token' } }
+      @access_token.expects(:get).with('/debug_token', params).raises(::OAuth2::Error.new(stub_everything('Faraday::Response')))
+      strategy.stubs(:access_token).returns(@access_token)
+      assert_raises(OmniAuth::Strategies::Facebook::AppIdMismatchError) { strategy.send(:build_access_token) {} }
     end
-  end
 
-  class MissingCodeInCookieRequestTest < TestCase
-    def setup(algo = nil)
-      super()
-      @payload = {
-        'algorithm' => algo || 'HMAC-SHA256',
-        'code' => nil,
-        'issued_at' => Time.now.to_i,
-        'user_id' => '123456'
-      }
-
-      @request.stubs(:cookies).returns({"fbsr_#{@client_id}" => signed_request(@payload, @client_secret)})
+    test 'fails when good token with missing scope' do
+      params = { params: { input_token: 'fake_token', access_token: 'other_token' } }
+      missing_scopes_response = stub_everything('Faraday::Response')
+      missing_scopes_response.stubs(:parsed).returns({ 'data' => {'scopes' => [] }})
+      @access_token.expects(:get).with('/debug_token', params).returns(missing_scopes_response)
+      assert_raises(OmniAuth::Strategies::Facebook::MissingScopesError) { strategy.send(:build_access_token) {} }
     end
 
-    test 'calls fail! when a code is not included in the cookie' do
-      strategy.expects(:fail!).times(1).with(:no_authorization_code, kind_of(OmniAuth::Strategies::Facebook::NoAuthorizationCodeError))
-      strategy.callback_phase
+    test 'succeeds when good token and scope' do
+      params = { params: { input_token: 'fake_token', access_token: 'other_token' } }
+      good_response = stub_everything('Faraday::Response')
+      good_response.stubs(:parsed).returns({ 'data' => {'scopes' => %w(public_profile email)}})
+      @access_token.expects(:get).with('/debug_token', params).returns(good_response)
+      assert_equal 'fake_token', strategy.send(:build_access_token).token
     end
   end
-
-  class UnknownAlgorithmInCookieRequestTest < TestCase
-    def setup
-      super()
-      @payload = {
-        'algorithm' => 'UNKNOWN-ALGO',
-        'code' => nil,
-        'issued_at' => Time.now.to_i,
-        'user_id' => '123456'
-      }
-
-      @request.stubs(:cookies).returns({"fbsr_#{@client_id}" => signed_request(@payload, @client_secret)})
+  # Fails when good token with missing scope
+  # Passes when param and good token
+  module VerifiedAccessTokenTests
+    module SignedRequestHelpers
+      def signed_request(payload, secret)
+        encoded_payload = base64_encode_url(MultiJson.encode(payload))
+        encoded_signature = base64_encode_url(signature(encoded_payload, secret))
+        [encoded_signature, encoded_payload].join('.')
+      end
+
+      def base64_encode_url(value)
+        Base64.encode64(value).tr('+/', '-_').gsub(/\n/, '')
+      end
+
+      def signature(payload, secret, algorithm = OpenSSL::Digest::SHA256.new)
+        OpenSSL::HMAC.digest(algorithm, secret, payload)
+      end
     end
 
-    test 'calls fail! when an algorithm is unknown' do
-      strategy.expects(:fail!).times(1).with(:unknown_signature_algorithm, kind_of(OmniAuth::Facebook::SignedRequest::UnknownSignatureAlgorithmError))
-      strategy.callback_phase
+    module SignedRequestTests
+      class TestCase < StrategyTestCase
+        include SignedRequestHelpers
+      end
+
+      class CookiePresentTest < TestCase
+        def setup(algo = nil)
+          super()
+          @payload = {
+            'algorithm' => algo || 'HMAC-SHA256',
+            'code' => 'm4c0d3z',
+            'issued_at' => Time.now.to_i,
+            'user_id' => '123456'
+          }
+
+          @request.stubs(:cookies).returns({"fbsr_#{@client_id}" => signed_request(@payload, @client_secret)})
+        end
+
+        test 'parses the access code out from the cookie' do
+          assert_equal @payload, strategy.send(:signed_request_from_cookie)
+        end
+
+        test 'throws an error if the algorithm is unknown' do
+          setup('UNKNOWN-ALGO')
+          assert_equal "unknown algorithm: UNKNOWN-ALGO", assert_raises(OmniAuth::Facebook::SignedRequest::UnknownSignatureAlgorithmError) { strategy.send(:signed_request_from_cookie) }.message
+        end
+      end
+
+      class EmptySignedRequestTest < TestCase
+        def setup
+          super
+          @request.stubs(:params).returns({'signed_request' => ''})
+        end
+
+        test 'empty param' do
+          assert_nil strategy.send(:signed_request_from_cookie)
+        end
+      end
+
+      class MissingCodeInCookieRequestTest < TestCase
+        def setup(algo = nil)
+          super()
+          @payload = {
+            'algorithm' => algo || 'HMAC-SHA256',
+            'code' => nil,
+            'issued_at' => Time.now.to_i,
+            'user_id' => '123456'
+          }
+
+          @request.stubs(:cookies).returns({"fbsr_#{@client_id}" => signed_request(@payload, @client_secret)})
+        end
+
+        test 'calls fail! when a code is not included in the cookie' do
+          strategy.expects(:fail!).times(1).with(:no_authorization_code, kind_of(OmniAuth::Strategies::Facebook::NoAuthorizationCodeError))
+          strategy.callback_phase
+        end
+      end
+
+      class UnknownAlgorithmInCookieRequestTest < TestCase
+        def setup
+          super()
+          @payload = {
+            'algorithm' => 'UNKNOWN-ALGO',
+            'code' => nil,
+            'issued_at' => Time.now.to_i,
+            'user_id' => '123456'
+          }
+
+          @request.stubs(:cookies).returns({"fbsr_#{@client_id}" => signed_request(@payload, @client_secret)})
+        end
+
+        test 'calls fail! when an algorithm is unknown' do
+          strategy.expects(:fail!).times(1).with(:unknown_signature_algorithm, kind_of(OmniAuth::Facebook::SignedRequest::UnknownSignatureAlgorithmError))
+          strategy.callback_phase
+        end
+      end
     end
   end
 end