Add support for x5t and x5t#S256 header

CHANGELOG.md

@@ -20,6 +20,7 @@ Take a look at the [upgrade guide](UPGRADING.md) for more details.
 - JWT::EncodedToken#verify! method that bundles signature and claim validation [#647](https://github.com/jwt/ruby-jwt/pull/647) ([@anakinj](https://github.com/anakinj))
 - Do not override the alg header if already given [#659](https://github.com/jwt/ruby-jwt/pull/659) ([@anakinj](https://github.com/anakinj))
 - Make `JWK::KeyFinder` compatible with `JWT::EncodedToken` [#663](https://github.com/jwt/ruby-jwt/pull/663) ([@anakinj](https://github.com/anakinj))
+- Add support for x5t header parameter for X.509 certificate thumbprint verification [#669](https://github.com/jwt/ruby-jwt/pull/669) ([@hieuk09](https://github.com/hieuk09))
 - Your contribution here
 
 **Fixes and enhancements:**

README.md

@@ -674,13 +674,14 @@ algorithms = jwks.map { |key| key[:alg] }.compact.uniq
 JWT.decode(token, nil, true, algorithms: algorithms, jwks: jwks)
 ```
 
-The `jwks` option can also be given as a lambda that evaluates every time a kid is resolved.
+The `jwks` option can also be given as a lambda that evaluates every time a key identifier is resolved.
 This can be used to implement caching of remotely fetched JWK Sets.
 
-If the requested `kid` is not found from the given set the loader will be called a second time with the `kid_not_found` option set to `true`.
+Key identifiers can be specified using `kid`, `x5t` or `x5c` header parameters.
+If the requested identifier is not found from the given set the loader will be called a second time with the `kid_not_found` option set to `true`.
 The application can choose to implement some kind of JWK cache invalidation or other mechanism to handle such cases.
 
-Tokens without a specified `kid` are rejected by default.
+Tokens without a specified key identifier (`kid`, `x5t` or `x5c`) are rejected by default.
 This behaviour may be overwritten by setting the `allow_nil_kid` option for `decode` to `true`.
 
 ```ruby

lib/jwt/base64.rb

@@ -13,6 +13,12 @@ def url_encode(str)
         ::Base64.urlsafe_encode64(str, padding: false)
       end
 
+      # Encode a string with Base64 complying with RFC 4648 (padded).
+      # @api private
+      def strict_encode(str)
+        ::Base64.strict_encode64(str)
+      end
+
       # Decode a string with URL-safe Base64 complying with RFC 4648.
       # @api private
       def url_decode(str)

lib/jwt/decode.rb

@@ -60,7 +60,8 @@ def verify_algo
 
     def set_key
       @key = find_key(&@keyfinder) if @keyfinder
-      @key = ::JWT::JWK::KeyFinder.new(jwks: @options[:jwks], allow_nil_kid: @options[:allow_nil_kid]).key_for(token.header['kid']) if @options[:jwks]
+      @key = ::JWT::JWK::KeyFinder.new(jwks: @options[:jwks], allow_nil_kid: @options[:allow_nil_kid]).call(token) if @options[:jwks]
+
       return unless (x5c_options = @options[:x5c])
 
       @key = X5cKeyFinder.new(x5c_options[:root_certificates], x5c_options[:crls]).from(token.header['x5c'])

lib/jwt/jwk/key_finder.rb

@@ -22,11 +22,10 @@ def initialize(options)
 
       # Returns the verification key for the given kid
       # @param [String] kid the key id
-      def key_for(kid)
-        raise ::JWT::DecodeError, 'No key id (kid) found from token headers' unless kid || @allow_nil_kid
-        raise ::JWT::DecodeError, 'Invalid type for kid header parameter' unless kid.nil? || kid.is_a?(String)
+      def key_for(kid, key_field = :kid)
+        raise ::JWT::DecodeError, "Invalid type for #{key_field} header parameter" unless kid.nil? || kid.is_a?(String)
 
-        jwk = resolve_key(kid)
+        jwk = resolve_key(kid, key_field)
 
         raise ::JWT::DecodeError, 'No keys found in jwks' unless @jwks.any?
         raise ::JWT::DecodeError, "Could not find public key for kid #{kid}" unless jwk
@@ -37,22 +36,36 @@ def key_for(kid)
       # Returns the key for the given token
       # @param [JWT::EncodedToken] token the token
       def call(token)
-        key_for(token.header['kid'])
+        kid = token.header['kid']
+        x5t = token.header['x5t']
+        x5c = token.header['x5c']
+
+        if kid
+          key_for(kid, :kid)
+        elsif x5t
+          key_for(x5t, :x5t)
+        elsif x5c
+          key_for(x5c, :x5c)
+        elsif @allow_nil_kid
+          key_for(kid)
+        else
+          raise ::JWT::DecodeError, 'No key id (kid) or x5t found from token headers'
+        end
       end
 
       private
 
-      def resolve_key(kid)
-        key_matcher = ->(key) { (kid.nil? && @allow_nil_kid) || key[:kid] == kid }
+      def resolve_key(kid, key_field)
+        key_matcher = ->(key) { (kid.nil? && @allow_nil_kid) || key[key_field] == kid }
 
         # First try without invalidation to facilitate application caching
-        @jwks ||= JWT::JWK::Set.new(@jwks_loader.call(kid: kid))
+        @jwks ||= JWT::JWK::Set.new(@jwks_loader.call(key_field => kid))
         jwk = @jwks.find { |key| key_matcher.call(key) }
 
         return jwk if jwk
 
         # Second try, invalidate for backwards compatibility
-        @jwks = JWT::JWK::Set.new(@jwks_loader.call(invalidate: true, kid_not_found: true, kid: kid))
+        @jwks = JWT::JWK::Set.new(@jwks_loader.call(invalidate: true, kid_not_found: true, key_field => kid))
         @jwks.find { |key| key_matcher.call(key) }
       end
     end

lib/jwt/jwk/rsa.rb

@@ -51,6 +51,9 @@ def verify_key
       def export(options = {})
         exported = parameters.clone
         exported.reject! { |k, _| RSA_PRIVATE_KEY_ELEMENTS.include? k } unless private? && options[:include_private] == true
+
+        exported[:x5t] = Base64.url_encode(OpenSSL::Digest::SHA1.new(rsa_key.to_der).digest) if options[:include_x5t]
+
         exported
       end
 
@@ -67,7 +70,7 @@ def key_digest
       def []=(key, value)
         raise ArgumentError, 'cannot overwrite cryptographic key attributes' if RSA_KEY_ELEMENTS.include?(key.to_sym)
 
-        super(key, value)
+        super
       end
 
       private

spec/jwt/jwk/decode_with_jwk_spec.rb

@@ -4,7 +4,8 @@
   describe '.decode for JWK usecase' do
     let(:keypair)       { test_pkey('rsa-2048-private.pem') }
     let(:jwk)           { JWT::JWK.new(keypair) }
-    let(:public_jwks) { { keys: [jwk.export, { kid: 'not_the_correct_one', kty: 'oct', k: 'secret' }] } }
+    let(:valid_key)     { jwk.export }
+    let(:public_jwks) { { keys: [valid_key, { kid: 'not_the_correct_one', kty: 'oct', k: 'secret' }] } }
     let(:token_payload) { { 'data' => 'something' } }
     let(:token_headers) { { kid: jwk.kid } }
     let(:algorithm)     { 'RS512' }
@@ -38,6 +39,15 @@
         end
       end
 
+      context 'and x5t is in the set' do
+        let(:valid_key) { jwk.export(include_x5t: true) }
+        let(:token_headers) { { x5t: Base64.urlsafe_encode64(OpenSSL::Digest::SHA1.new(keypair.to_der).digest, padding: false) } }
+        it 'is able to decode the token' do
+          payload, _header = described_class.decode(signed_token, nil, true, { algorithms: [algorithm], jwks: public_jwks })
+          expect(payload).to eq(token_payload)
+        end
+      end
+
       context 'no keys are found in the set' do
         let(:public_jwks) { { keys: [] } }
         it 'raises an exception' do
@@ -51,7 +61,7 @@
         let(:token_headers) { {} }
         it 'raises an exception' do
           expect { described_class.decode(signed_token, nil, true, { algorithms: [algorithm], jwks: public_jwks }) }.to raise_error(
-            JWT::DecodeError, 'No key id (kid) found from token headers'
+            JWT::DecodeError, 'No key id (kid) or x5t found from token headers'
           )
         end
       end

spec/jwt/jwk/rsa_spec.rb

@@ -67,6 +67,16 @@
         expect(subject).to include(:kty, :n, :e, :kid, :d, :p, :q, :dp, :dq, :qi)
       end
     end
+
+    context 'when x5t option is requested' do
+      subject { described_class.new(keypair).export(include_x5t: true) }
+      let(:keypair) { rsa_key }
+      it 'returns a hash with x5t thumbprint' do
+        expect(subject).to be_a Hash
+        expect(subject).to include(:kty, :n, :e, :kid, :x5t)
+        expect(subject[:x5t]).to be_a String
+      end
+    end
   end
 
   describe '.kid' do