Adds an implementation of JWT signing to ServiceAccountCredentials

.rubocop_todo.yml

@@ -1,15 +1,15 @@
 # This configuration was generated by `rubocop --auto-gen-config`
-# on 2015-02-25 04:34:33 -0800 using RuboCop version 0.28.0.
+# on 2015-03-06 19:51:00 -0800 using RuboCop version 0.28.0.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
 # versions of RuboCop, may require this file to be generated again.
 
-# Offense count: 1
+# Offense count: 3
 Metrics/AbcSize:
-  Max: 16
+  Max: 24
 
-# Offense count: 1
+# Offense count: 3
 # Configuration parameters: CountComments.
 Metrics/MethodLength:
   Max: 11

lib/googleauth/service_account.rb

@@ -29,6 +29,7 @@
 
 require 'googleauth/signet'
 require 'googleauth/credentials_loader'
+require 'jwt'
 require 'multi_json'
 
 module Google
@@ -43,6 +44,8 @@ module Google
     #
     # cf [Application Default Credentials](http://goo.gl/mkAHpZ)
     class ServiceAccountCredentials < Signet::OAuth2::Client
+      JWT_AUD_URI_KEY = :jwt_aud_uri
+      AUTH_METADATA_KEY = Signet::OAuth2::AUTH_METADATA_KEY
       TOKEN_CRED_URI = 'https://www.googleapis.com/oauth2/v3/token'
       extend CredentialsLoader
 
@@ -67,6 +70,34 @@ module Google
               issuer: client_email,
               signing_key: OpenSSL::PKey::RSA.new(private_key))
       end
+
+      # Extends the superclass behaviour to construct a jwt token if the
+      # google jwt uri key is present in the input hash.
+      #
+      # The jwt is used as the authentication token.
+      def apply!(a_hash, opts = {})
+        jwt_aud_uri = a_hash.delete(JWT_AUD_URI_KEY)
+        unless jwt_aud_uri.nil?
+          jwt_token = new_jwt_token(jwt_aud_uri, opts)
+          a_hash[AUTH_METADATA_KEY] = "Bearer #{jwt_token}"
+          return a_hash
+        end
+        super
+      end
+
+      # Creates a jwt uri token.
+      def new_jwt_token(jwt_aud_uri, options = {})
+        now = Time.new
+        skew = options[:skew] || 60
+        assertion = {
+          'iss' => issuer,
+          'sub' => issuer,
+          'aud' => jwt_aud_uri,
+          'exp' => (now + expiry).to_i,
+          'iat' => (now - skew).to_i
+        }
+        JWT.encode(assertion, signing_key, signing_algorithm)
+      end
     end
   end
 end

spec/googleauth/apply_auth_examples.rb

@@ -46,9 +46,9 @@ def build_access_token_json(token)
                       'expires_in' => 3600)
 end
 
-WANTED_AUTH_KEY = :Authorization
-
 shared_examples 'apply/apply! are OK' do
+  WANTED_AUTH_KEY = :Authorization
+
   # tests that use these examples need to define
   #
   # @client which should be an auth client

spec/googleauth/service_account_spec.rb

@@ -44,6 +44,8 @@ describe Google::Auth::ServiceAccountCredentials do
   ServiceAccountCredentials = Google::Auth::ServiceAccountCredentials
   CredentialsLoader = Google::Auth::CredentialsLoader
 
+  let(:client_email) { 'app@developer.gserviceaccount.com' }
+
   before(:example) do
     @key = OpenSSL::PKey::RSA.new(2048)
     @client = ServiceAccountCredentials.new(
@@ -69,7 +71,7 @@ describe Google::Auth::ServiceAccountCredentials do
     cred_json = {
       private_key_id: 'a_private_key_id',
       private_key: @key.to_pem,
-      client_email: 'app@developer.gserviceaccount.com',
+      client_email: client_email,
       client_id: 'app.apps.googleusercontent.com',
       type: 'service_account'
     }
@@ -78,6 +80,67 @@ describe Google::Auth::ServiceAccountCredentials do
 
   it_behaves_like 'apply/apply! are OK'
 
+  context 'when jwt_aud_uri is present' do
+    WANTED_AUTH_KEY = ServiceAccountCredentials::AUTH_METADATA_KEY
+    JWT_AUD_URI_KEY = ServiceAccountCredentials::JWT_AUD_URI_KEY
+    let(:test_uri) { 'https://www.googleapis.com/myservice' }
+    let(:auth_prefix) { 'Bearer ' }
+
+    def expect_is_encoded_jwt(hdr)
+      expect(hdr).to_not be_nil
+      expect(hdr.start_with?(auth_prefix)).to be true
+      authorization = hdr[auth_prefix.length..-1]
+      payload, _ = JWT.decode(authorization, @key.public_key)
+      expect(payload['aud']).to eq(test_uri)
+      expect(payload['iss']).to eq(client_email)
+    end
+
+    describe '#apply!' do
+      it 'should update the target hash with a jwt token' do
+        md = { foo: 'bar' }
+        md[JWT_AUD_URI_KEY] = test_uri
+        @client.apply!(md)
+        auth_header = md[WANTED_AUTH_KEY]
+        expect_is_encoded_jwt(auth_header)
+        expect(md[JWT_AUD_URI_KEY]).to be_nil
+      end
+    end
+
+    describe 'updater_proc' do
+      it 'should provide a proc that updates a hash with a jwt token' do
+        md = { foo: 'bar' }
+        md[JWT_AUD_URI_KEY] = test_uri
+        the_proc = @client.updater_proc
+        got = the_proc.call(md)
+        auth_header = got[WANTED_AUTH_KEY]
+        expect_is_encoded_jwt(auth_header)
+        expect(got[JWT_AUD_URI_KEY]).to be_nil
+        expect(md[JWT_AUD_URI_KEY]).to_not be_nil
+      end
+    end
+
+    describe '#apply' do
+      it 'should not update the original hash with a jwt token' do
+        md = { foo: 'bar' }
+        md[JWT_AUD_URI_KEY] = test_uri
+        the_proc = @client.updater_proc
+        got = the_proc.call(md)
+        auth_header = md[WANTED_AUTH_KEY]
+        expect(auth_header).to be_nil
+        expect(got[JWT_AUD_URI_KEY]).to be_nil
+        expect(md[JWT_AUD_URI_KEY]).to_not be_nil
+      end
+
+      it 'should add a jwt token to the returned hash' do
+        md = { foo: 'bar' }
+        md[JWT_AUD_URI_KEY] = test_uri
+        got = @client.apply(md)
+        auth_header = got[WANTED_AUTH_KEY]
+        expect_is_encoded_jwt(auth_header)
+      end
+    end
+  end
+
   describe '#from_env' do
     before(:example) do
       @var_name = CredentialsLoader::ENV_VAR