Extract the auth library into its own project

- adds no new functionality beyond the initial attempt at providing
  Usable Auth constructors.

- adds enough packaging metadata to be able to export this library as a gem.

- next steps:
  complete usable auth implemntation of Application Default Credentials.

lib/googleauth/compute_engine.rb

@@ -0,0 +1,69 @@
+# 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 'faraday'
+require 'googleauth/signet'
+
+module Google
+  # Module Auth provides classes that provide Google-specific authorization
+  # used to access Google APIs.
+  module Auth
+    # Extends Signet::OAuth2::Client so that the auth token is obtained from
+    # the GCE metadata server.
+    class GCECredentials < Signet::OAuth2::Client
+      # The IP Address is used in the URIs to speed up failures on non-GCE
+      # systems.
+      COMPUTE_AUTH_TOKEN_URI = 'http://169.254.169.254/computeMetadata/v1/'\
+                               'instance/service-accounts/default/token'
+      COMPUTE_CHECK_URI = 'http://169.254.169.254'
+
+      # Detect if this appear to be a GCE instance, by checking if metadata
+      # is available
+      def self.on_gce?(options = {})
+        c = options[:connection] || Faraday.default_connection
+        resp = c.get(COMPUTE_CHECK_URI)
+        return false unless resp.status == 200
+        return false unless resp.headers.key?('Metadata-Flavor')
+        return resp.headers['Metadata-Flavor'] == 'Google'
+      rescue Faraday::ConnectionFailed
+        return false
+      end
+
+      # Overrides the super class method to change how access tokens are
+      # fetched.
+      def fetch_access_token(options = {})
+        c = options[:connection] || Faraday.default_connection
+        c.headers = { 'Metadata-Flavor' => 'Google' }
+        resp = c.get(COMPUTE_AUTH_TOKEN_URI)
+        Signet::OAuth2.parse_credentials(resp.body,
+                                         resp.headers['content-type'])
+      end
+    end
+  end
+end

lib/googleauth/service_account.rb

@@ -0,0 +1,71 @@
+# 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 'multi_json'
+require 'openssl'
+
+# Reads the private key and client email fields from service account JSON key.
+def read_json_key(json_key_io)
+  json_key = MultiJson.load(json_key_io.read)
+  fail 'missing client_email' unless json_key.key?('client_email')
+  fail 'missing private_key' unless json_key.key?('private_key')
+  [json_key['private_key'], json_key['client_email']]
+end
+
+module Google
+  # Module Auth provides classes that provide Google-specific authorization
+  # used to access Google APIs.
+  module Auth
+    # Authenticates requests using Google's Service Account credentials.
+    #
+    # This class provides a simpler surface to the behavior in
+    # Signet::OAuth2::Client.  It allows authorizing requests directly using
+    # credentials from a json key file downloaded from the developer console
+    # (via 'Generate new Json Key').
+    #
+    # cf [Application Default Credentials](http://goo.gl/mkAHpZ)
+    class ServiceAccountCredentials < Signet::OAuth2::Client
+      TOKEN_CRED_URI = 'https://www.googleapis.com/oauth2/v3/token'
+
+      # Initializes a ServiceAccountCredentials.
+      #
+      # @param scope [string|array] the scope(s) to access
+      # @param json_key_io [IO] an IO from which the JSON key can be read
+      def initialize(scope, json_key_io)
+        private_key, client_email = read_json_key(json_key_io)
+        super(token_credential_uri: TOKEN_CRED_URI,
+              audience: TOKEN_CRED_URI,  # TODO: confirm this
+              scope: scope,
+              issuer: client_email,
+              signing_key: OpenSSL::PKey::RSA.new(private_key))
+      end
+    end
+  end
+end

lib/googleauth/signet.rb

@@ -0,0 +1,63 @@
+# 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 'signet/oauth_2/client'
+
+module Signet
+  # OAuth2 supports OAuth2 authentication.
+  module OAuth2
+    AUTH_METADATA_KEY = :Authorization
+    # Signet::OAuth2::Client creates an OAuth2 client
+    #
+    # This reopens Client to add #apply and #apply! methods which update a
+    # hash with the fetched authentication token.
+    class Client
+      # Updates a_hash updated with the authentication token
+      def apply!(a_hash, opts = {})
+        # fetch the access token there is currently not one, or if the client
+        # has expired
+        fetch_access_token!(opts) if access_token.nil? || expired?
+        a_hash[AUTH_METADATA_KEY] = "Bearer #{access_token}"
+      end
+
+      # Returns a clone of a_hash updated with the authentication token
+      def apply(a_hash, opts = {})
+        a_copy = a_hash.clone
+        apply!(a_copy, opts)
+        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

lib/googleauth/version.rb

@@ -0,0 +1,36 @@
+# Copyright 2014, 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.
+
+module Google
+  # Module Auth provides classes that provide Google-specific authorization
+  # used to access Google APIs.
+  module Auth
+    VERSION = '0.1.0'
+  end
+end