add method #pkce_valid? for validating pkce

README.md

@@ -44,6 +44,11 @@ pkce_challenge.code_verifier # a dynamically created cryptographically random ke
 pkce_challenge.code_challenge # a BASE64-URL-encoded string of the SHA256 hash of the code verifier
 ```
 
+Additionally you can verify provided code_challenge based on code_verifier
+```ruby
+PkceChallenge.pkce_valid?(code_verifier: code_verifier, code_challenge: code_challenge)
+```
+
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

lib/pkce_challenge.rb

@@ -23,4 +23,23 @@ class LengthOutOfRangeError < StandardError; end
   def self.challenge(options = {})
     PkceChallenge::Challenge.new(options)
   end
+
+  # Validates code challenge and verfiier
+  #
+  # Example:
+  #   >> PkceChallenge.pkce_valid?(code_verifier: '', code_challenge: '')
+  #   => true
+  #
+  # == Parameters:
+  # code_verifier::
+  #   A String containing code_verifier
+  # code_challenge::
+  #   A String containing code_challenge
+  #
+  # == Returns:
+  # An instance of Bool
+  #
+  def self.pkce_valid?(code_verifier:, code_challenge:)
+    PkceChallenge::Challenge.new.pkce_valid?(code_verifier: code_verifier, code_challenge: code_challenge)
+  end
 end

lib/pkce_challenge/challenge.rb

@@ -19,6 +19,10 @@ def code_challenge
       @code_challenge ||= generate_pkce_challenge
     end
 
+    def pkce_valid?(code_verifier:, code_challenge:)
+      code_challenge == generate_pkce_challenge(code_verifier)
+    end
+
     # constants definition
 
     CHAR_LENGTH = {
@@ -39,8 +43,8 @@ def generate_code_verifier
       urlsafe_base64(SecureRandom.base64((length * 3) / 4))
     end
 
-    def generate_pkce_challenge
-      urlsafe_base64(Digest::SHA256.base64digest(code_verifier))
+    def generate_pkce_challenge(verifier=nil)
+      urlsafe_base64(Digest::SHA256.base64digest(verifier || code_verifier))
     end
 
     def urlsafe_base64(base64_str)

spec/pkce_challenge_spec.rb

@@ -28,4 +28,16 @@
       expect { invalid.code_verifier }.to raise_error(PkceChallenge::LengthOutOfRangeError)
     end
   end
+
+  describe "#pkce_valid?" do
+    let(:challenge) { PkceChallenge.challenge }
+
+    it "should returns true/false based on provided data" do
+      code_challenge = challenge.code_challenge
+      code_verifier = challenge.verifier
+
+      expect(PkceChallenge.pkce_valid?(code_verifier: code_verifier, code_challenge: code_challenge)).to be_truthy
+      expect(PkceChallenge.pkce_valid?(code_verifier: code_verifier, code_challenge: 'random')).to be_falsy
+    end
+  end
 end