diff --git a/Gemfile b/Gemfile
index da9c01851..b4ecf0e22 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,6 +1,6 @@
 source :rubygems
 
-gem 'signet', '>= 0.3.1'
+gem 'signet', '>= 0.3.4'
 gem 'addressable', '>= 2.2.3'
 gem 'autoparse', '>= 0.3.1'
 gem 'faraday', '~> 0.7.0'
diff --git a/lib/google/api_client/service_account.rb b/lib/google/api_client/service_account.rb
new file mode 100644
index 000000000..7d8caad78
--- /dev/null
+++ b/lib/google/api_client/service_account.rb
@@ -0,0 +1,134 @@
+# Copyright 2010 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+require 'jwt'
+require 'signet/oauth_2/client'
+
+module Google
+  class APIClient
+    ##
+    # Helper for loading keys from the PKCS12 files downloaded when
+    # setting up service accounts at the APIs Console.
+    module PKCS12
+      
+      ##
+      # Loads a key from PKCS12 file, assuming a single private key
+      # is present.
+      #
+      # @param [String] keyfile
+      #    Path of the PKCS12 file to load. If not a path to an actual file,
+      #    assumes the string is the content of the file itself. 
+      # @param [String] passphrase
+      #   Passphrase for unlocking the private key
+      #
+      # @return [OpenSSL::PKey] The private key for signing assertions.
+      def self.load_key(keyfile, passphrase)
+        begin
+          if File.exists?(keyfile)
+            content = File.read(keyfile)
+          else
+            content = keyfile
+          end  
+          pkcs12 = OpenSSL::PKCS12.new(content, passphrase)
+          return pkcs12.key
+        rescue OpenSSL::PKCS12::PKCS12Error
+          raise ArgumentError.new("Invalid keyfile or passphrase")
+        end
+      end
+    end
+
+    ##
+    # Generates access tokens using the JWT assertion profile. Requires a
+    # service account & access to the private key.
+    class JWTAsserter
+      attr_accessor :issuer, :expiry
+      attr_reader :scope
+      attr_writer :key
+
+      ##
+      # Initializes the asserter for a service account.
+      #
+      # @param [String] issuer
+      #    Name/ID of the client issuing the assertion
+      # @param [String or Array] scope
+      #   Scopes to authorize. May be a space delimited string or array of strings
+      # @param [OpenSSL::PKey]
+      #   RSA private key for signing assertions
+      def initialize(issuer, scope, key)
+        self.issuer = issuer
+        self.scope = scope
+        self.expiry = 60 # 1 min default        
+        self.key = key
+      end
+
+      ##
+      # Set the scopes to authorize
+      #
+      # @param [String or Array] scope
+      #   Scopes to authorize. May be a space delimited string or array of strings
+      def scope=(new_scope)
+        case new_scope
+        when Array
+          @scope = new_scope.join(' ')
+        when String
+          @scope = new_scope
+        when nil
+          @scope = ''
+        else
+          raise TypeError, "Expected Array or String, got #{new_scope.class}"
+        end
+      end
+      
+      ##
+      # Builds & signs the assertion.
+      # 
+      # @param [String] person
+      #   Email address of a user, if requesting a token to act on their behalf
+      # @return [String] Encoded JWT
+      def to_jwt(person=nil)
+        now = Time.new        
+        assertion = {
+          "iss" => @issuer,
+          "scope" => self.scope,
+          "aud" => "https://accounts.google.com/o/oauth2/token",
+          "exp" => (now + expiry).to_i,
+          "iat" => now.to_i
+        }
+        assertion['prn'] = person unless person.nil?
+        return JWT.encode(assertion, @key, "RS256")
+      end
+
+      ##
+      # Request a new access token.
+      # 
+      # @param [String] person
+      #   Email address of a user, if requesting a token to act on their behalf
+      # @param [Hash] options
+      #   Pass through to Signet::OAuth2::Client.fetch_access_token
+      # @return [Signet::OAuth2::Client] Access token 
+      #
+      # @see Signet::OAuth2::Client.fetch_access_token
+      def authorize(person = nil, options={})
+        assertion = self.to_jwt(person)
+        authorization = Signet::OAuth2::Client.new(
+          :token_credential_uri => 'https://accounts.google.com/o/oauth2/token'
+        )
+        authorization.grant_type = 'urn:ietf:params:oauth:grant-type:jwt-bearer'
+        authorization.extension_parameters = { :assertion => assertion }
+        authorization.fetch_access_token!(options)
+        return authorization
+      end
+    end
+  end
+end
diff --git a/spec/google/api_client/service_account_spec.rb b/spec/google/api_client/service_account_spec.rb
new file mode 100644
index 000000000..d10499414
--- /dev/null
+++ b/spec/google/api_client/service_account_spec.rb
@@ -0,0 +1,58 @@
+# Copyright 2012 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+require 'spec_helper'
+
+require 'google/api_client'
+
+describe Google::APIClient::JWTAsserter do
+  
+  before do
+    @key = OpenSSL::PKey::RSA.new 2048
+  end
+  
+  it 'should generate valid JWTs' do
+    asserter = Google::APIClient::JWTAsserter.new('client1', 'scope1 scope2', @key)
+    jwt = asserter.to_jwt
+    jwt.should_not == nil  
+    
+    claim = JWT.decode(jwt, @key.public_key, true)
+    claim["iss"].should == 'client1'
+    claim["scope"].should == 'scope1 scope2'
+  end
+  
+  it 'should send valid access token request' do
+    stubs = Faraday::Adapter::Test::Stubs.new do |stub|
+      stub.post('/o/oauth2/token') do |env|
+        params = Addressable::URI.form_unencode(env[:body])
+        JWT.decode(params.assoc("assertion").last, @key.public_key)
+        params.assoc("grant_type").should == ['grant_type','urn:ietf:params:oauth:grant-type:jwt-bearer']
+        [200, {}, '{
+          "access_token" : "1/abcdef1234567890",
+          "token_type" : "Bearer",
+          "expires_in" : 3600
+        }']
+      end
+    end
+    connection = Faraday.new(:url => 'https://accounts.google.com') do |builder|
+      builder.adapter(:test, stubs)
+    end
+  
+    asserter = Google::APIClient::JWTAsserter.new('client1', 'scope1 scope2', @key)
+    auth = asserter.authorize(nil, { :connection => connection})
+    auth.should_not == nil?
+    auth.access_token.should == "1/abcdef1234567890"
+  end
+end
+