Add support for JWKS decoding of JWT's (#68)

README.md

@@ -201,4 +201,6 @@ the provider settings, so you will need to clear the browser's
   * Vault login failed. Expired or missing OAuth state.
 ```
 
-
+# Decoding JWKS based tokens
+To decode JWKS based tokens, set the astral.yml "jwks_url" parameter to the 
+jwks endpoint of your auth provider.

app/lib/jwt/jwks_decoder.rb

@@ -0,0 +1,40 @@
+require "open-uri"
+module Jwt
+  class JwksDecoder
+    def initialize(url)
+      @url = url
+    end
+
+    def configured?(config)
+      !@url.nil?
+    end
+
+    # Decode a JWT token signed with JWKS
+    def decode(token)
+      jwks = get_jwks_keyset_from_configured_url
+      jwks = filter_out_non_signing_keys(jwks)
+      body = JWT.decode(token, nil, true,
+                        algorithms: get_algorithms_from_keyset(jwks),
+                        jwks: jwks)[0]
+      Identity.new(body)
+    rescue => e
+      Rails.logger.warn "Unable to decode token: #{e}"
+      nil
+    end
+
+    private
+
+    def get_jwks_keyset_from_configured_url
+      jwks_json = URI.open(@url) { |f| f.read }
+      JWT::JWK::Set.new(JSON.parse(jwks_json))
+    end
+
+    def filter_out_non_signing_keys(jwks)
+      jwks.filter { |k| k[:use] == "sig" }
+    end
+
+    def get_algorithms_from_keyset(jwks)
+      jwks.map { |k| k[:alg] }.compact.uniq
+    end
+  end
+end

app/lib/jwt/secret_decoder.rb

@@ -0,0 +1,20 @@
+module Jwt
+  class SecretDecoder
+    def initialize(secret)
+      @secret = secret
+    end
+
+    def configured?(config)
+      !@secret.nil?
+    end
+
+    def decode(token)
+      # Decode a JWT access token using the configured base.
+      body = JWT.decode(token, Config[:jwt_signing_key])[0]
+      Identity.new(body)
+    rescue => e
+      Rails.logger.warn "Unable to decode token: #{e}"
+      nil
+    end
+  end
+end

app/lib/services/auth.rb

@@ -2,22 +2,11 @@ module Services
   class Auth
     class << self
       def authenticate!(token)
-        identity = decode(token)
+        identity = Utils::DecoderFactory.get(Config).decode(token)
         raise AuthError unless identity
         # TODO verify identity with authority?
         identity
       end
-
-      private
-
-      def decode(token)
-        # Decode a JWT access token using the configured base.
-        body = JWT.decode(token, Config[:jwt_signing_key])[0]
-        Identity.new(body)
-      rescue => e
-        Rails.logger.warn "Unable to decode token: #{e}"
-        nil
-      end
     end
   end
 end

app/lib/utils/decoder_factory.rb

@@ -0,0 +1,23 @@
+module Utils
+  class DecoderFactory
+    cattr_reader :decoders
+    class << self
+      # Any new decoders should be added here:
+      @@decoders = [ Jwt::JwksDecoder.new(Config[:jwks_url]),
+                     Jwt::SecretDecoder.new(Config[:jwt_signing_key]) ]
+
+      def get(config)
+        configured_decoders = getConfiguredDecoders(config)
+        if configured_decoders.length != 1
+          raise "Exactly one decoder must be configured"
+        end
+        configured_decoders.first
+      end
+
+      private
+      def getConfiguredDecoders(config)
+        decoders.filter { |c| c.configured?(config) }
+      end
+    end
+  end
+end

config/astral.yml

@@ -21,6 +21,9 @@ shared:
 
   jwt_signing_key:
 
+  # define this to allow jwks decoding of JWT's
+  jwks_url:
+
   # When using AppRegistry for Domain Ownership information
   app_registry_addr:
   app_registry_token:

test/lib/jwt/jwks_decoder_test.rb

@@ -0,0 +1,39 @@
+require "test_helper"
+require "jwt"
+require "openssl"
+require "json"
+require "tempfile"
+
+class JwksDecoderTest < ActiveSupport::TestCase
+  test ".decode returns correct identity" do
+    jwk = generate_jwks_signing_key
+    token = generate_jwks_token(jwk)
+    keyset_path = generate_jwks_keyset(jwk)
+
+    identity = Jwt::JwksDecoder.new(keyset_path).decode(token)
+    assert_equal "[email protected]", identity.sub
+    assert_equal "astral", identity.aud
+  end
+
+  private
+
+  def generate_jwks_signing_key
+    optional_parameters = { kid: "1", use: "sig", alg: "RS256" }
+    jwk = JWT::JWK.new(OpenSSL::PKey::RSA.new(2048), optional_parameters)
+  end
+
+  def generate_jwks_token(jwk)
+    payload = { "sub"=>"[email protected]", "name"=>"John Doe", "iat"=>1516239022,
+               "groups"=>[ "group1", "group2" ], "aud"=>"astral" }
+
+    JWT.encode(payload, jwk.signing_key, jwk[:alg], kid: jwk[:kid])
+  end
+
+  def generate_jwks_keyset(jwk)
+    jwks_hash = JWT::JWK::Set.new(jwk).export
+    f = Tempfile.new
+    f.write(JSON.pretty_generate(jwks_hash))
+    f.close
+    f.path
+  end
+end

test/lib/jwt/secret_decoder_test.rb

@@ -0,0 +1,10 @@
+require "test_helper"
+
+class SecretDecoderTest < ActiveSupport::TestCase
+  test ".decode returns correct identity" do
+    identity = Jwt::SecretDecoder.new(Config[:jwt_signing_key]).
+                 decode(jwt_authorized)
+    assert_equal "[email protected]", identity.sub
+    assert_equal "astral", identity.aud
+  end
+end

test/lib/utils/decoder_factory_test.rb

@@ -0,0 +1,29 @@
+require "test_helper"
+
+class DecoderFactoryTest < ActiveSupport::TestCase
+  test ".get returns configured decoder" do
+    decoders = [ UnconfiguredDecoder.new, ConfiguredDecoder.new ]
+    Utils::DecoderFactory.stub :decoders, decoders do
+      decoder = Utils::DecoderFactory.get({})
+      assert decoder.instance_of?(ConfiguredDecoder)
+    end
+  end
+
+  test ".get recognizes invalid config" do
+    decoders = [ ConfiguredDecoder.new, ConfiguredDecoder.new ]
+    Utils::DecoderFactory.stub :decoders, decoders do
+      assert_raises(
+        RuntimeError, "Exactly one decoder must be configured") do
+        decoder = Utils::DecoderFactory.get({})
+      end
+    end
+  end
+
+  class ConfiguredDecoder
+    def configured?(c) = true
+  end
+
+  class UnconfiguredDecoder
+    def configured?(c) = false
+  end
+end