added test

.rubocop.yml

@@ -44,5 +44,5 @@ Style/StringLiterals:
 Style/TrailingCommaInArguments:
   EnforcedStyleForMultiline: comma
 
-Style/TrailingCommaInLiteral:
+Style/TrailingCommaInArrayLiteral:
   EnforcedStyleForMultiline: comma

lib/omniauth-oauth2.rb

@@ -1,2 +1,2 @@
-require "omniauth-oauth2/version" # rubocop:disable FileName
+require "omniauth-oauth2/version"
 require "omniauth/strategies/oauth2"

lib/omniauth/strategies/oauth2.rb

@@ -106,14 +106,14 @@ def options_for(option)
       end
 
       # constant-time comparison algorithm to prevent timing attacks
-      def secure_compare(a, b)
-        return false unless a.bytesize == b.bytesize
+      def secure_compare(string_a, string_b)
+        return false unless string_a.bytesize == string_b.bytesize
 
-        l = a.unpack "C#{a.bytesize}"
+        l = string_a.unpack "C#{string_a.bytesize}"
 
         res = 0
-        b.each_byte { |byte| res |= byte ^ l.shift }
-        res == 0
+        string_b.each_byte { |byte| res |= byte ^ l.shift }
+        res.zero?
       end
 
       # An error that is indicated in the OAuth 2.0 callback.

spec/omniauth/strategies/oauth2_spec.rb

@@ -87,6 +87,16 @@ def app
       instance.callback_phase
     end
   end
+
+  describe "#secure_params" do
+    subject { fresh_strategy }
+
+    it "returns true when the two inputs are the same and false otherwise" do
+      instance = subject.new("abc", "def")
+      expect(instance.send(:secure_compare, "a", "a")).to be true
+      expect(instance.send(:secure_compare, "b", "a")).to be false
+    end
+  end
 end
 
 describe OmniAuth::Strategies::OAuth2::CallbackError do