Stop using the term invalidate to not assume the app always has a cache

CHANGELOG.md

@@ -13,6 +13,7 @@
 **Fixes and enhancements:**
 - Bring back the old Base64 (RFC2045) deocode mechanisms [#488](https://github.com/jwt/ruby-jwt/pull/488) ([@anakinj](https://github.com/anakinj)).
 - Rescue RbNaCl exception for EdDSA wrong key [#491](https://github.com/jwt/ruby-jwt/pull/491) ([@n-studio](https://github.com/n-studio)).
+- New parameter name for cases when kid is not found using key loader [#501](https://github.com/jwt/ruby-jwt/pull/501) ([@anakinj](https://github.com/anakinj)).
 - Your contribution here
 
 ## [v2.4.1](https://github.com/jwt/ruby-jwt/tree/v2.4.1) (2022-06-07)

README.md

@@ -546,30 +546,41 @@ end
 
 ### JSON Web Key (JWK)
 
-JWK is a JSON structure representing a cryptographic key. Currently only supports RSA, EC and HMAC keys.
+JWK is a JSON structure representing a cryptographic key. Currently only supports RSA, EC and HMAC keys. The `jwks` option can be given as a lambda that evaluates every time a kid is resolved.
 
-```ruby
-jwk = JWT::JWK.new(OpenSSL::PKey::RSA.new(2048), "optional-kid")
-payload, headers = { data: 'data' }, { kid: jwk.kid }
-
-token = JWT.encode(payload, jwk.keypair, 'RS512', headers)
+If the 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`. The application can choose to implement some kind of JWK cache invalidation or other mechanism to handle such cases.
 
-# The jwk loader would fetch the set of JWKs from a trusted source
-jwk_loader = ->(options) do
-  @cached_keys = nil if options[:invalidate] # need to reload the keys
-  @cached_keys ||= { keys: [jwk.export] }
-end
+```ruby
+  jwk = JWT::JWK.new(OpenSSL::PKey::RSA.new(2048), 'optional-kid')
+  payload = { data: 'data' }
+  headers = { kid: jwk.kid }
+
+  token = JWT.encode(payload, jwk.keypair, 'RS512', headers)
+
+  # The jwk loader would fetch the set of JWKs from a trusted source,
+  # to avoid malicious requests triggering cache invalidations there needs to be some kind of grace time or other logic for determining the validity of the invalidation.
+  # This example only allows cache invalidations ever 5 minutes
+  jwk_loader = ->(options) do
+    if options[:kid_not_found] && @cache_last_update < Time.now.to_i - 300
+      logger.info("Invalidating JWK cache. #{options[:kid]} not found from previous cache")
+      @cached_keys = nil
+    end
+    @cached_keys ||= begin
+      @cache_last_update = Time.now.to_i
+      { keys: [jwk.export] }
+    end
+  end
 
-begin
-  JWT.decode(token, nil, true, { algorithms: ['RS512'], jwks: jwk_loader})
-rescue JWT::JWKError
-  # Handle problems with the provided JWKs
-rescue JWT::DecodeError
-  # Handle other decode related issues e.g. no kid in header, no matching public key found etc.
-end
+  begin
+    JWT.decode(token, nil, true, { algorithms: ['RS512'], jwks: jwk_loader })
+  rescue JWT::JWKError
+    # Handle problems with the provided JWKs
+  rescue JWT::DecodeError
+    # Handle other decode related issues e.g. no kid in header, no matching public key found etc.
+  end
 ```
 
-or by passing JWK as a simple Hash
+or by passing the JWKs as a simple Hash
 
 ```
 jwks = { keys: [{ ... }] } # keys accepts both of string and symbol

lib/jwt/jwk/key_finder.rb

@@ -28,7 +28,7 @@ def resolve_key(kid)
         return jwk if jwk
 
         if reloadable?
-          load_keys(invalidate: true)
+          load_keys(invalidate: true, kid_not_found: true, kid: kid) # invalidate for backwards compatibility
           return find_key(kid)
         end
 

spec/integration/readme_examples_spec.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require 'logger'
+
 RSpec.describe 'README.md code test' do
   context 'algorithm usage' do
     let(:payload) { { data: 'test' } }
@@ -273,21 +275,53 @@
       end.not_to raise_error
     end
 
-    it 'JWK' do
-      jwk = JWT::JWK.new(OpenSSL::PKey::RSA.new(2048))
-      payload = { data: 'data' }
-      headers = { kid: jwk.kid }
+    context 'The JWK loader example' do
+      let(:logger_output) { StringIO.new }
+      let(:logger) { Logger.new(logger_output) }
+
+      it 'works as expected' do
+        jwk = JWT::JWK.new(OpenSSL::PKey::RSA.new(2048), 'optional-kid')
+        payload = { data: 'data' }
+        headers = { kid: jwk.kid }
+
+        token = JWT.encode(payload, jwk.keypair, 'RS512', headers)
+
+        # The jwk loader would fetch the set of JWKs from a trusted source,
+        # to avoid malicious invalidations some kind of protection needs to be implemented.
+        # This example only allows cache invalidations ever 5 minutes
+        jwk_loader = ->(options) do
+          if options[:kid_not_found] && @cache_last_update < Time.now.to_i - 300
+            logger.info("Invalidating JWK cache. #{options[:kid]} not found from previous cache")
+            @cached_keys = nil
+          end
+          @cached_keys ||= begin
+            @cache_last_update = Time.now.to_i
+            { keys: [jwk.export] }
+          end
+        end
 
-      token = JWT.encode(payload, jwk.keypair, 'RS512', headers)
+        begin
+          JWT.decode(token, nil, true, { algorithms: ['RS512'], jwks: jwk_loader })
+        rescue JWT::JWKError
+          # Handle problems with the provided JWKs
+        rescue JWT::DecodeError
+          # Handle other decode related issues e.g. no kid in header, no matching public key found etc.
+        end
+
+        ## This is not in the example but verifies that the cache is invalidated after 5 minutes
+        jwk = JWT::JWK.new(OpenSSL::PKey::RSA.new(2048), 'new-kid')
+
+        payload = { data: 'data' }
+        headers = { kid: jwk.kid }
+
+        token = JWT.encode(payload, jwk.keypair, 'RS512', headers)
+        @cache_last_update = Time.now.to_i - 301
 
-      # The jwk loader would fetch the set of JWKs from a trusted source
-      jwk_loader = ->(options) do
-        @cached_keys = nil if options[:invalidate] # need to reload the keys
-        @cached_keys ||= { keys: [jwk.export] }
-      end
-      expect do
         JWT.decode(token, nil, true, { algorithms: ['RS512'], jwks: jwk_loader })
-      end.not_to raise_error
+        JWT.decode(token, nil, true, { algorithms: ['RS512'], jwks: jwk_loader })
+
+        expect(logger_output.string.chomp).to match(/^I, .* : Invalidating JWK cache. new-kid not found from previous cache/)
+      end
     end
 
     it 'JWK with thumbprint as kid via symbol' do