diff --git a/lib/googleauth/iam.rb b/lib/googleauth/iam.rb
new file mode 100644
index 0000000..3632744
--- /dev/null
+++ b/lib/googleauth/iam.rb
@@ -0,0 +1,75 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+require 'googleauth/signet'
+require 'googleauth/credentials_loader'
+require 'multi_json'
+
+module Google
+  # Module Auth provides classes that provide Google-specific authorization
+  # used to access Google APIs.
+  module Auth
+    # Authenticates requests using IAM credentials.
+    class IAMCredentials
+      SELECTOR_KEY = 'x-goog-iam-authority-selector'
+      TOKEN_KEY = 'x-goog-iam-authorization-token'
+
+      # Initializes an IAMCredentials.
+      #
+      # @param selector the IAM selector.
+      # @param token the IAM token.
+      def initialize(selector, token)
+        fail TypeError unless selector.is_a? String
+        fail TypeError unless token.is_a? String
+        @selector = selector
+        @token = token
+      end
+
+      # Adds the credential fields to the hash.
+      def apply!(a_hash)
+        a_hash[SELECTOR_KEY] = @selector
+        a_hash[TOKEN_KEY] = @token
+        a_hash
+      end
+
+      # Returns a clone of a_hash updated with the authoriation header
+      def apply(a_hash)
+        a_copy = a_hash.clone
+        apply!(a_copy)
+        a_copy
+      end
+
+      # Returns a reference to the #apply method, suitable for passing as
+      # a closure
+      def updater_proc
+        lambda(&method(:apply))
+      end
+    end
+  end
+end
diff --git a/spec/googleauth/iam_spec.rb b/spec/googleauth/iam_spec.rb
new file mode 100644
index 0000000..f7b2b3e
--- /dev/null
+++ b/spec/googleauth/iam_spec.rb
@@ -0,0 +1,80 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+spec_dir = File.expand_path(File.join(File.dirname(__FILE__)))
+$LOAD_PATH.unshift(spec_dir)
+$LOAD_PATH.uniq!
+
+require 'googleauth/iam'
+
+describe Google::Auth::IAMCredentials do
+  IAMCredentials = Google::Auth::IAMCredentials
+  let(:test_selector) { 'the-test-selector' }
+  let(:test_token) { 'the-test-token' }
+  let(:test_creds) { IAMCredentials.new(test_selector, test_token) }
+
+  describe '#apply!' do
+    it 'should update the target hash with the iam values' do
+      md = { foo: 'bar' }
+      test_creds.apply!(md)
+      expect(md[IAMCredentials::SELECTOR_KEY]).to eq test_selector
+      expect(md[IAMCredentials::TOKEN_KEY]).to eq test_token
+      expect(md[:foo]).to eq 'bar'
+    end
+  end
+
+  describe 'updater_proc' do
+    it 'should provide a proc that updates a hash with the iam values' do
+      md = { foo: 'bar' }
+      the_proc = test_creds.updater_proc
+      got = the_proc.call(md)
+      expect(got[IAMCredentials::SELECTOR_KEY]).to eq test_selector
+      expect(got[IAMCredentials::TOKEN_KEY]).to eq test_token
+      expect(got[:foo]).to eq 'bar'
+    end
+  end
+
+  describe '#apply' do
+    it 'should not update the original hash with the iam values' do
+      md = { foo: 'bar' }
+      test_creds.apply(md)
+      expect(md[IAMCredentials::SELECTOR_KEY]).to be_nil
+      expect(md[IAMCredentials::TOKEN_KEY]).to be_nil
+      expect(md[:foo]).to eq 'bar'
+    end
+
+    it 'should return a with the iam values' do
+      md = { foo: 'bar' }
+      got = test_creds.apply(md)
+      expect(got[IAMCredentials::SELECTOR_KEY]).to eq test_selector
+      expect(got[IAMCredentials::TOKEN_KEY]).to eq test_token
+      expect(got[:foo]).to eq 'bar'
+    end
+  end
+end