diff --git a/CHANGELOG.md b/CHANGELOG.md
index a720072c..4ef39d2c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -97,6 +97,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Added
   - [#684](https://github.com/binarylogic/authlogic/pull/684) - Use cookies
     only when available. Support for `ActionController::API`
+  - [#728](https://github.com/binarylogic/authlogic/pull/728) - Allow
+    single_access_token to be supplied using Headers in addition to Params.
 - Fixed
   - [#725](https://github.com/binarylogic/authlogic/pull/725) - `NoMethodError`
     when setting `sign_cookie` or `encrypt_cookie` before `controller` is
diff --git a/lib/authlogic/session/base.rb b/lib/authlogic/session/base.rb
index 716b658a..2ba59f86 100644
--- a/lib/authlogic/session/base.rb
+++ b/lib/authlogic/session/base.rb
@@ -236,6 +236,20 @@ def initialize(session)
     #
     # You can modify all of this behavior with the Config sub module.
     #
+    # Headers
+    # =======
+    #
+    # This module is responsible for authenticating the user via headers, which requires
+    # setting HTTP header, for example, the following curl command:
+    #
+    #   curl -H "user_credentials: 4LiXF7FiGUppIPubBPey" https://www.domain.com
+    #
+    # Notice the token in the header parameter, this is a single access token. This header's
+    # method operates exactly as the params method.
+    #
+    # You can modify all of this behavior with the Config sub module.
+    #
+    # Disabled by default. To enable, set a non-nil headers_key.
     # Perishable Token
     # ================
     #
@@ -410,6 +424,7 @@ def self.#{method}(*filter_list, &block)
 
       # `persist` callbacks, in order of priority
       persist :persist_by_params
+      persist :persist_by_headers
       persist :persist_by_cookie
       persist :persist_by_session
       persist :persist_by_http_auth, if: :persist_by_http_auth?
@@ -857,6 +872,24 @@ def params_key(value = nil)
         end
         alias params_key= params_key
 
+        # Works exactly like cookie_key, but for headers. So a user can login via
+        # headers just like a cookie or a session. Your URL would look like:
+        #
+        #   curl -H "user_credentials: 4LiXF7FiGUppIPubBPey" https://www.domain.com
+        #
+        # You can change the "user_credentials" key above with this
+        # configuration option. Keep in mind, just like cookie_key, if you
+        # supply an id the id will be appended to the front. Check out
+        # cookie_key for more details. Also checkout the "Single Access /
+        # Private Feeds Access" section in the README.
+        #
+        # * <tt>Default:</tt> nil
+        # * <tt>Accepts:</tt> String
+        def headers_key(value = nil)
+          rw_config(:headers_key, value)
+        end
+        alias headers_key= headers_key
+
         # Works exactly like login_field, but for the password instead. Returns
         # :password if a login_field exists.
         #
@@ -1876,21 +1909,33 @@ def params_credentials
         controller.params[params_key]
       end
 
+      def headers_credentials
+        # Setting headers_key to nil is the accepted way to disable
+        # single_access_token in headers.
+        return nil if headers_key.nil?
+        controller.request.headers[headers_key]
+      end
+
       def params_enabled?
-        if !params_credentials || !klass.column_names.include?("single_access_token")
-          return false
-        end
-        if controller.responds_to_single_access_allowed?
-          return controller.single_access_allowed?
-        end
-        params_enabled_by_allowed_request_types?
+        params_credentials && single_access_token_enabled?
+      end
+
+      def headers_enabled?
+        headers_credentials && single_access_token_enabled?
+      end
+
+      def single_access_token_enabled?
+        return false unless klass.column_names.include?("single_access_token")
+        return controller.single_access_allowed? if controller.responds_to_single_access_allowed?
+
+        single_access_token_allowed_by_request_type?
       end
 
-      def params_enabled_by_allowed_request_types?
-        case single_access_allowed_request_types
-        when Array
-          single_access_allowed_request_types.include?(controller.request_content_type) ||
-            single_access_allowed_request_types.include?(:all)
+      def single_access_token_allowed_by_request_type?
+        if single_access_allowed_request_types.is_a?(Array)
+          Set.new(single_access_allowed_request_types).intersect?(
+            Set[controller.request_content_type, :all]
+          )
         else
           %i[all any].include?(single_access_allowed_request_types)
         end
@@ -1900,6 +1945,16 @@ def params_key
         build_key(self.class.params_key)
       end
 
+      def headers_key
+        # Rack servers uppercase header names, convert hyphens to underscores,
+        # and prefix with "HTTP_" to comply with CGI. We transform the key in
+        # the same way Rails does:
+        # https://github.com/rails/rails/blob/6-0-stable/actionpack/lib/action_dispatch/http/headers.rb#L123-L126
+        key = build_key(self.class.headers_key)
+        return nil if key.nil?
+        "HTTP_" + key.upcase.tr("-", "_")
+      end
+
       def password_field
         self.class.password_field
       end
@@ -1919,10 +1974,17 @@ def persist_by_cookie
       end
 
       def persist_by_params
-        return false unless params_enabled?
+        persist_by_single_access_token(params_credentials) if params_enabled?
+      end
+
+      def persist_by_headers
+        persist_by_single_access_token(headers_credentials) if headers_enabled?
+      end
+
+      def persist_by_single_access_token(credentials)
         self.unauthorized_record = search_for_record(
           "find_by_single_access_token",
-          params_credentials
+          credentials
         )
         self.single_access = valid?
       end
diff --git a/lib/authlogic/test_case/mock_api_controller.rb b/lib/authlogic/test_case/mock_api_controller.rb
index 3fe4e38e..852c50cb 100644
--- a/lib/authlogic/test_case/mock_api_controller.rb
+++ b/lib/authlogic/test_case/mock_api_controller.rb
@@ -26,6 +26,10 @@ def params
         @params ||= {}
       end
 
+      def headers
+        @headers ||= {}
+      end
+
       def request
         @request ||= MockRequest.new(self)
       end
diff --git a/lib/authlogic/test_case/mock_request.rb b/lib/authlogic/test_case/mock_request.rb
index 6848d17f..1d8b6b14 100644
--- a/lib/authlogic/test_case/mock_request.rb
+++ b/lib/authlogic/test_case/mock_request.rb
@@ -19,6 +19,10 @@ def format
         controller.request_content_type if controller.respond_to? :request_content_type
       end
 
+      def headers
+        @headers ||= {}
+      end
+
       def ip
         controller&.respond_to?(:env) &&
           controller.env.is_a?(Hash) &&
diff --git a/test/session_test/params_test.rb b/test/session_test/single_access_token_test.rb
similarity index 71%
rename from test/session_test/params_test.rb
rename to test/session_test/single_access_token_test.rb
index 5d280f13..6a7843b5 100644
--- a/test/session_test/params_test.rb
+++ b/test/session_test/single_access_token_test.rb
@@ -3,9 +3,11 @@
 require "test_helper"
 
 module SessionTest
-  module ParamsTest
+  module SingleAccessTokenTest
     class ConfigTest < ActiveSupport::TestCase
       def test_params_key
+        assert_equal UserSession.cookie_key, UserSession.params_key
+
         UserSession.params_key = "my_params_key"
         assert_equal "my_params_key", UserSession.params_key
 
@@ -13,6 +15,16 @@ def test_params_key
         assert_equal "user_credentials", UserSession.params_key
       end
 
+      def test_headers_key
+        assert_equal nil, UserSession.headers_key
+
+        UserSession.headers_key = "my_headers_key"
+        assert_equal "my_headers_key", UserSession.headers_key
+
+        UserSession.headers_key "user_credentials"
+        assert_equal "user_credentials", UserSession.headers_key
+      end
+
       def test_single_access_allowed_request_types
         UserSession.single_access_allowed_request_types = ["my request type"]
         assert_equal ["my request type"], UserSession.single_access_allowed_request_types
@@ -28,11 +40,21 @@ def test_single_access_allowed_request_types
 
     class InstanceMethodsTest < ActiveSupport::TestCase
       def test_persist_persist_by_params
+        assert_persist_by(:params)
+      end
+
+      def test_persist_persist_by_headers
+        # Since default headers_key is nil, set for the test.
+        UserSession.send("headers_key=", "user_credentials")
+        assert_persist_by(:headers)
+      end
+
+      def assert_persist_by(headers_or_params)
         ben = users(:ben)
         session = UserSession.new
 
         refute session.persisting?
-        set_params_for(ben)
+        send("set_#{headers_or_params}_for", ben)
 
         refute session.persisting?
         refute session.unauthorized_record
diff --git a/test/test_helper.rb b/test/test_helper.rb
index f2e3de8c..d55d36c2 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -274,6 +274,14 @@ def unset_params
       controller.params["user_credentials"] = nil
     end
 
+    def set_headers_for(user)
+      controller.request.headers["HTTP_USER_CREDENTIALS"] = user.single_access_token
+    end
+
+    def unset_headers
+      controller.request.headers["HTTP_USER_CREDENTIALS"] = nil
+    end
+
     def set_request_content_type(type)
       controller.request_content_type = type
     end