diff --git a/src/ruby/bin/apis/pubsub_demo.rb b/src/ruby/bin/apis/pubsub_demo.rb
index 6656a561309fd52d1b9eca88a95201e607aa70a2..9bb324ff6463d84461fdff613a24f7449eca414e 100755
--- a/src/ruby/bin/apis/pubsub_demo.rb
+++ b/src/ruby/bin/apis/pubsub_demo.rb
@@ -31,10 +31,9 @@
 
 # pubsub_demo demos accesses the Google PubSub API via its gRPC interface
 #
-# TODO: update the Usage once the usable auth gem is available
-# $ SSL_CERT_FILE=<path/to/ssl/certs> \
+# $ GOOGLE_APPLICATION_CREDENTIALS=<path_to_service_account_key_file> \
+#   SSL_CERT_FILE=<path/to/ssl/certs> \
 #   path/to/pubsub_demo.rb \
-#   --service_account_key_file=<path_to_service_account> \
 #   [--action=<chosen_demo_action> ]
 #
 # There are options related to the chosen action, see #parse_args below.
@@ -49,6 +48,7 @@ $LOAD_PATH.unshift(this_dir) unless $LOAD_PATH.include?(this_dir)
 require 'optparse'
 
 require 'grpc'
+require 'googleauth'
 require 'google/protobuf'
 
 require 'google/protobuf/empty'
@@ -59,7 +59,9 @@ require 'tech/pubsub/proto/pubsub_services'
 def load_prod_cert
   fail 'could not find a production cert' if ENV['SSL_CERT_FILE'].nil?
   p "loading prod certs from #{ENV['SSL_CERT_FILE']}"
-  File.open(ENV['SSL_CERT_FILE']).read
+  File.open(ENV['SSL_CERT_FILE']) do |f|
+    return f.read
+  end
 end
 
 # creates a SSL Credentials from the production certificates.
@@ -68,14 +70,9 @@ def ssl_creds
 end
 
 # Builds the metadata authentication update proc.
-#
-# TODO: replace this once the ruby usable auth repo is available.
 def auth_proc(opts)
-  if GRPC::Auth::GCECredentials.on_gce?
-    return GRPC::Auth::GCECredentials.new.updater_proc
-  end
-  fd = StringIO.new(File.read(opts.oauth_key_file))
-  GRPC::Auth::ServiceAccountCredentials.new(opts.oauth_scope, fd).updater_proc
+  auth_creds = Google::Auth.get_application_default(opts.oauth_scope)
+  return auth_creds.updater_proc
 end
 
 # Creates a stub for accessing the publisher service.
@@ -216,14 +213,14 @@ class NamedActions
 end
 
 # Args is used to hold the command line info.
-Args = Struct.new(:host, :oauth_scope, :oauth_key_file, :port, :action,
-                  :project_id, :topic_name, :sub_name)
+Args = Struct.new(:host, :oauth_scope, :port, :action, :project_id, :topic_name,
+                  :sub_name)
 
 # validates the the command line options, returning them as an Arg.
 def parse_args
   args = Args.new('pubsub-staging.googleapis.com',
                   'https://www.googleapis.com/auth/pubsub',
-                  nil, 443, 'list_some_topics', 'stoked-keyword-656')
+                   443, 'list_some_topics', 'stoked-keyword-656')
   OptionParser.new do |opts|
     opts.on('--oauth_scope scope',
             'Scope for OAuth tokens') { |v| args['oauth_scope'] = v }
@@ -233,10 +230,6 @@ def parse_args
     opts.on('--server_port SERVER_PORT', 'server port') do |v|
       args.port = v
     end
-    opts.on('--service_account_key_file PATH',
-            'Path to the service account json key file') do |v|
-      args.oauth_key_file = v
-    end
 
     # instance_methods(false) gives only the methods defined in that class.
     scenes = NamedActions.instance_methods(false).map { |t| t.to_s }
@@ -257,15 +250,11 @@ def parse_args
 end
 
 def _check_args(args)
-  %w(host port action).each do |a|
+  %w(host port action oauth_scope).each do |a|
     if args[a].nil?
       raise OptionParser::MissingArgument.new("please specify --#{a}")
     end
   end
-  if args['oauth_key_file'].nil? || args['oauth_scope'].nil?
-    fail(OptionParser::MissingArgument,
-         'please specify both of --service_account_key_file and --oauth_scope')
-  end
   args
 end
 
diff --git a/src/ruby/bin/interop/interop_client.rb b/src/ruby/bin/interop/interop_client.rb
index 380ceb11df09c990b426c42c430bdae89cd8e309..b0b24b949f25326f8da8b9f4f80731a09271d767 100755
--- a/src/ruby/bin/interop/interop_client.rb
+++ b/src/ruby/bin/interop/interop_client.rb
@@ -48,6 +48,7 @@ require 'minitest'
 require 'minitest/assertions'
 
 require 'grpc'
+require 'googleauth'
 require 'google/protobuf'
 
 require 'test/cpp/interop/test_services'
@@ -56,7 +57,7 @@ require 'test/cpp/interop/empty'
 
 require 'signet/ssl_config'
 
-include GRPC::Auth
+AUTH_ENV = Google::Auth::ServiceAccountCredentials::ENV_VAR
 
 # loads the certificates used to access the test server securely.
 def load_test_certs
@@ -101,22 +102,14 @@ def create_stub(opts)
     }
 
     # Add service account creds if specified
-    if %w(all service_account_creds).include?(opts.test_case)
+    wants_creds = %w(all compute_engine_creds service_account_creds)
+    if wants_creds.include?(opts.test_case)
       unless opts.oauth_scope.nil?
-        fd = StringIO.new(File.read(opts.oauth_key_file))
-        logger.info("loading oauth certs from #{opts.oauth_key_file}")
-        auth_creds = ServiceAccountCredentials.new(opts.oauth_scope, fd)
+        auth_creds = Google::Auth.get_application_default(opts.oauth_scope)
         stub_opts[:update_metadata] = auth_creds.updater_proc
       end
     end
 
-    # Add compute engine creds if specified
-    if %w(all compute_engine_creds).include?(opts.test_case)
-      unless opts.oauth_scope.nil?
-        stub_opts[:update_metadata] = GCECredentials.new.update_proc
-      end
-    end
-
     logger.info("... connecting securely to #{address}")
     Grpc::Testing::TestService::Stub.new(address, **stub_opts)
   else
@@ -193,11 +186,11 @@ class NamedTests
 
   def service_account_creds
     # ignore this test if the oauth options are not set
-    if @args.oauth_scope.nil? || @args.oauth_key_file.nil?
+    if @args.oauth_scope.nil?
       p 'NOT RUN: service_account_creds; no service_account settings'
       return
     end
-    json_key = File.read(@args.oauth_key_file)
+    json_key = File.read(ENV[AUTH_ENV])
     wanted_email = MultiJson.load(json_key)['client_email']
     resp = perform_large_unary(fill_username: true,
                                fill_oauth_scope: true)
@@ -285,7 +278,7 @@ end
 
 # Args is used to hold the command line info.
 Args = Struct.new(:default_service_account, :host, :host_override,
-                  :oauth_scope, :oauth_key_file, :port, :secure, :test_case,
+                  :oauth_scope, :port, :secure, :test_case,
                   :use_test_ca)
 
 # validates the the command line options, returning them as a Hash.
@@ -302,10 +295,6 @@ def parse_args
             'email address of the default service account') do |v|
       args['default_service_account'] = v
     end
-    opts.on('--service_account_key_file PATH',
-            'Path to the service account json key file') do |v|
-      args['oauth_key_file'] = v
-    end
     opts.on('--server_host_override HOST_OVERRIDE',
             'override host via a HTTP header') do |v|
       args['host_override'] = v
@@ -333,10 +322,6 @@ def _check_args(args)
       fail(OptionParser::MissingArgument, "please specify --#{arg}")
     end
   end
-  if args['oauth_key_file'].nil? ^ args['oauth_scope'].nil?
-    fail(OptionParser::MissingArgument,
-         'please specify both of --service_account_key_file and --oauth_scope')
-  end
   args
 end
 
diff --git a/src/ruby/grpc.gemspec b/src/ruby/grpc.gemspec
index bc59c234e5a4ecf1246344ef61641917855183b2..25a3ff5ce27a4956c64ca7b3da05b5d189b7e1d2 100755
--- a/src/ruby/grpc.gemspec
+++ b/src/ruby/grpc.gemspec
@@ -22,6 +22,7 @@ Gem::Specification.new do |s|
 
   s.add_dependency 'faraday', '~> 0.9'
   s.add_dependency 'google-protobuf', '~> 3.0.0alpha.1.1'
+  s.add_dependency 'googleauth', '~> 0.1'
   s.add_dependency 'logging', '~> 1.8'
   s.add_dependency 'jwt', '~> 1.2.1'
   s.add_dependency 'minitest', '~> 5.4'  # reqd for interop tests
diff --git a/src/ruby/lib/grpc.rb b/src/ruby/lib/grpc.rb
index a2a609f59ee96d8dbb93cb7aaf3ddcd428e782c3..dd02ef7666a8d1875931860e19c444882ac40dc2 100644
--- a/src/ruby/lib/grpc.rb
+++ b/src/ruby/lib/grpc.rb
@@ -27,8 +27,6 @@
 # (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 'grpc/auth/compute_engine.rb'
-require 'grpc/auth/service_account.rb'
 require 'grpc/errors'
 require 'grpc/grpc'
 require 'grpc/logconfig'
diff --git a/src/ruby/lib/grpc/auth/compute_engine.rb b/src/ruby/lib/grpc/auth/compute_engine.rb
deleted file mode 100644
index 5cb1e1a4dcfaa26b56077e52059bc4b6f463d94f..0000000000000000000000000000000000000000
--- a/src/ruby/lib/grpc/auth/compute_engine.rb
+++ /dev/null
@@ -1,67 +0,0 @@
-# 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 'grpc/auth/signet'
-
-module GRPC
-  # Module Auth provides classes that provide Google-specific authentication
-  # used to access Google gRPC services.
-  module Auth
-    # Extends Signet::OAuth2::Client so that the auth token is obtained from
-    # the GCE metadata server.
-    class GCECredentials < Signet::OAuth2::Client
-      COMPUTE_AUTH_TOKEN_URI = 'http://metadata/computeMetadata/v1/'\
-                               'instance/service-accounts/default/token'
-      COMPUTE_CHECK_URI = 'http://metadata.google.internal'
-
-      # 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
diff --git a/src/ruby/lib/grpc/auth/service_account.rb b/src/ruby/lib/grpc/auth/service_account.rb
deleted file mode 100644
index 14b81a9e034f9527caf46146390b36f2930b867c..0000000000000000000000000000000000000000
--- a/src/ruby/lib/grpc/auth/service_account.rb
+++ /dev/null
@@ -1,66 +0,0 @@
-# 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 'grpc/auth/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 GRPC
-  # Module Auth provides classes that provide Google-specific authentication
-  # used to access Google gRPC services.
-  module Auth
-    # Authenticates requests using Google's Service Account credentials.
-    # (cf https://developers.google.com/accounts/docs/OAuth2ServiceAccount)
-    class ServiceAccountCredentials < Signet::OAuth2::Client
-      TOKEN_CRED_URI = 'https://www.googleapis.com/oauth2/v3/token'
-      AUDIENCE = TOKEN_CRED_URI
-
-      # 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: AUDIENCE,
-              scope: scope,
-              issuer: client_email,
-              signing_key: OpenSSL::PKey::RSA.new(private_key))
-      end
-    end
-  end
-end
diff --git a/src/ruby/lib/grpc/auth/signet.rb b/src/ruby/lib/grpc/auth/signet.rb
deleted file mode 100644
index a8bce1255c239b8463e610ec9ec7a46cb8b32171..0000000000000000000000000000000000000000
--- a/src/ruby/lib/grpc/auth/signet.rb
+++ /dev/null
@@ -1,67 +0,0 @@
-# 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
-  # Signet::OAuth2 supports OAuth2 authentication.
-  module OAuth2
-    AUTH_METADATA_KEY = :Authorization
-    # Signet::OAuth2::Client creates an OAuth2 client
-    #
-    # Here client is re-opened to add the #apply and #apply! methods which
-    # update a hash map with the fetched authentication token
-    #
-    # Eventually, this change may be merged into signet itself, or some other
-    # package that provides Google-specific auth via signet, and this extension
-    # will be unnecessary.
-    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
diff --git a/src/ruby/spec/auth/apply_auth_examples.rb b/src/ruby/spec/auth/apply_auth_examples.rb
deleted file mode 100644
index 09b393026f02f888c13e3d5ff13492e28d8d6d06..0000000000000000000000000000000000000000
--- a/src/ruby/spec/auth/apply_auth_examples.rb
+++ /dev/null
@@ -1,163 +0,0 @@
-# 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 'faraday'
-require 'spec_helper'
-
-def build_json_response(payload)
-  [200,
-   { 'Content-Type' => 'application/json; charset=utf-8' },
-   MultiJson.dump(payload)]
-end
-
-WANTED_AUTH_KEY = :Authorization
-
-shared_examples 'apply/apply! are OK' do
-  # tests that use these examples need to define
-  #
-  # @client which should be an auth client
-  #
-  # @make_auth_stubs, which should stub out the expected http behaviour of the
-  # auth client
-  describe '#fetch_access_token' do
-    it 'should set access_token to the fetched value' do
-      token = '1/abcdef1234567890'
-      stubs = make_auth_stubs with_access_token: token
-      c = Faraday.new do |b|
-        b.adapter(:test, stubs)
-      end
-
-      @client.fetch_access_token!(connection: c)
-      expect(@client.access_token).to eq(token)
-      stubs.verify_stubbed_calls
-    end
-  end
-
-  describe '#apply!' do
-    it 'should update the target hash with fetched access token' do
-      token = '1/abcdef1234567890'
-      stubs = make_auth_stubs with_access_token: token
-      c = Faraday.new do |b|
-        b.adapter(:test, stubs)
-      end
-
-      md = { foo: 'bar' }
-      @client.apply!(md, connection: c)
-      want = { :foo => 'bar', WANTED_AUTH_KEY => "Bearer #{token}" }
-      expect(md).to eq(want)
-      stubs.verify_stubbed_calls
-    end
-  end
-
-  describe 'updater_proc' do
-    it 'should provide a proc that updates a hash with the access token' do
-      token = '1/abcdef1234567890'
-      stubs = make_auth_stubs with_access_token: token
-      c = Faraday.new do |b|
-        b.adapter(:test, stubs)
-      end
-
-      md = { foo: 'bar' }
-      the_proc = @client.updater_proc
-      got = the_proc.call(md, connection: c)
-      want = { :foo => 'bar', WANTED_AUTH_KEY => "Bearer #{token}" }
-      expect(got).to eq(want)
-      stubs.verify_stubbed_calls
-    end
-  end
-
-  describe '#apply' do
-    it 'should not update the original hash with the access token' do
-      token = '1/abcdef1234567890'
-      stubs = make_auth_stubs with_access_token: token
-      c = Faraday.new do |b|
-        b.adapter(:test, stubs)
-      end
-
-      md = { foo: 'bar' }
-      @client.apply(md, connection: c)
-      want = { foo: 'bar' }
-      expect(md).to eq(want)
-      stubs.verify_stubbed_calls
-    end
-
-    it 'should add the token to the returned hash' do
-      token = '1/abcdef1234567890'
-      stubs = make_auth_stubs with_access_token: token
-      c = Faraday.new do |b|
-        b.adapter(:test, stubs)
-      end
-
-      md = { foo: 'bar' }
-      got = @client.apply(md, connection: c)
-      want = { :foo => 'bar', WANTED_AUTH_KEY => "Bearer #{token}" }
-      expect(got).to eq(want)
-      stubs.verify_stubbed_calls
-    end
-
-    it 'should not fetch a new token if the current is not expired' do
-      token = '1/abcdef1234567890'
-      stubs = make_auth_stubs with_access_token: token
-      c = Faraday.new do |b|
-        b.adapter(:test, stubs)
-      end
-
-      n = 5 # arbitrary
-      n.times do |_t|
-        md = { foo: 'bar' }
-        got = @client.apply(md, connection: c)
-        want = { :foo => 'bar', WANTED_AUTH_KEY => "Bearer #{token}" }
-        expect(got).to eq(want)
-      end
-      stubs.verify_stubbed_calls
-    end
-
-    it 'should fetch a new token if the current one is expired' do
-      token_1 = '1/abcdef1234567890'
-      token_2 = '2/abcdef1234567890'
-
-      [token_1, token_2].each do |t|
-        stubs = make_auth_stubs with_access_token: t
-        c = Faraday.new do |b|
-          b.adapter(:test, stubs)
-        end
-        md = { foo: 'bar' }
-        got = @client.apply(md, connection: c)
-        want = { :foo => 'bar', WANTED_AUTH_KEY => "Bearer #{t}" }
-        expect(got).to eq(want)
-        stubs.verify_stubbed_calls
-        @client.expires_at -= 3601 # default is to expire in 1hr
-      end
-    end
-  end
-end
diff --git a/src/ruby/spec/auth/compute_engine_spec.rb b/src/ruby/spec/auth/compute_engine_spec.rb
deleted file mode 100644
index c43214d08610305b0908ac725943f2bc38b241ee..0000000000000000000000000000000000000000
--- a/src/ruby/spec/auth/compute_engine_spec.rb
+++ /dev/null
@@ -1,108 +0,0 @@
-# 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 'apply_auth_examples'
-require 'faraday'
-require 'grpc/auth/compute_engine'
-require 'spec_helper'
-
-describe GRPC::Auth::GCECredentials do
-  MD_URI = '/computeMetadata/v1/instance/service-accounts/default/token'
-  GCECredentials = GRPC::Auth::GCECredentials
-
-  before(:example) do
-    @client = GCECredentials.new
-  end
-
-  def make_auth_stubs(with_access_token: '')
-    Faraday::Adapter::Test::Stubs.new do |stub|
-      stub.get(MD_URI) do |env|
-        headers = env[:request_headers]
-        expect(headers['Metadata-Flavor']).to eq('Google')
-        build_json_response(
-            'access_token' => with_access_token,
-            'token_type' => 'Bearer',
-            'expires_in' => 3600)
-      end
-    end
-  end
-
-  it_behaves_like 'apply/apply! are OK'
-
-  describe '#on_gce?' do
-    it 'should be true when Metadata-Flavor is Google' do
-      stubs = Faraday::Adapter::Test::Stubs.new do |stub|
-        stub.get('/') do |_env|
-          [200,
-           { 'Metadata-Flavor' => 'Google' },
-           '']
-        end
-      end
-      c = Faraday.new do |b|
-        b.adapter(:test, stubs)
-      end
-      expect(GCECredentials.on_gce?(connection: c)).to eq(true)
-      stubs.verify_stubbed_calls
-    end
-
-    it 'should be false when Metadata-Flavor is not Google' do
-      stubs = Faraday::Adapter::Test::Stubs.new do |stub|
-        stub.get('/') do |_env|
-          [200,
-           { 'Metadata-Flavor' => 'NotGoogle' },
-           '']
-        end
-      end
-      c = Faraday.new do |b|
-        b.adapter(:test, stubs)
-      end
-      expect(GCECredentials.on_gce?(connection: c)).to eq(false)
-      stubs.verify_stubbed_calls
-    end
-
-    it 'should be false if the response is not 200' do
-      stubs = Faraday::Adapter::Test::Stubs.new do |stub|
-        stub.get('/') do |_env|
-          [404,
-           { 'Metadata-Flavor' => 'Google' },
-           '']
-        end
-      end
-      c = Faraday.new do |b|
-        b.adapter(:test, stubs)
-      end
-      expect(GCECredentials.on_gce?(connection: c)).to eq(false)
-      stubs.verify_stubbed_calls
-    end
-  end
-end
diff --git a/src/ruby/spec/auth/service_account_spec.rb b/src/ruby/spec/auth/service_account_spec.rb
deleted file mode 100644
index 2f14a1ae053260d00b04c4293dbc057ac2f7e080..0000000000000000000000000000000000000000
--- a/src/ruby/spec/auth/service_account_spec.rb
+++ /dev/null
@@ -1,75 +0,0 @@
-# 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 'apply_auth_examples'
-require 'grpc/auth/service_account'
-require 'jwt'
-require 'multi_json'
-require 'openssl'
-require 'spec_helper'
-
-describe GRPC::Auth::ServiceAccountCredentials do
-  before(:example) do
-    @key = OpenSSL::PKey::RSA.new(2048)
-    cred_json = {
-      private_key_id: 'a_private_key_id',
-      private_key: @key.to_pem,
-      client_email: 'app@developer.gserviceaccount.com',
-      client_id: 'app.apps.googleusercontent.com',
-      type: 'service_account'
-    }
-    cred_json_text = MultiJson.dump(cred_json)
-    @client = GRPC::Auth::ServiceAccountCredentials.new(
-        'https://www.googleapis.com/auth/userinfo.profile',
-        StringIO.new(cred_json_text))
-  end
-
-  def make_auth_stubs(with_access_token: '')
-    Faraday::Adapter::Test::Stubs.new do |stub|
-      stub.post('/oauth2/v3/token') do |env|
-        params = Addressable::URI.form_unencode(env[:body])
-        _claim, _header = JWT.decode(params.assoc('assertion').last,
-                                     @key.public_key)
-        want = ['grant_type', 'urn:ietf:params:oauth:grant-type:jwt-bearer']
-        expect(params.assoc('grant_type')).to eq(want)
-        build_json_response(
-          'access_token' => with_access_token,
-          'token_type' => 'Bearer',
-          'expires_in' => 3600
-        )
-      end
-    end
-  end
-
-  it_behaves_like 'apply/apply! are OK'
-end
diff --git a/src/ruby/spec/auth/signet_spec.rb b/src/ruby/spec/auth/signet_spec.rb
deleted file mode 100644
index 1712edf29614061a25fc15faa2b1e3ea45ef75d9..0000000000000000000000000000000000000000
--- a/src/ruby/spec/auth/signet_spec.rb
+++ /dev/null
@@ -1,70 +0,0 @@
-# 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 'apply_auth_examples'
-require 'grpc/auth/signet'
-require 'jwt'
-require 'openssl'
-require 'spec_helper'
-
-describe Signet::OAuth2::Client do
-  before(:example) do
-    @key = OpenSSL::PKey::RSA.new(2048)
-    @client = Signet::OAuth2::Client.new(
-        token_credential_uri: 'https://accounts.google.com/o/oauth2/token',
-        scope: 'https://www.googleapis.com/auth/userinfo.profile',
-        issuer: 'app@example.com',
-        audience: 'https://accounts.google.com/o/oauth2/token',
-        signing_key: @key
-      )
-  end
-
-  def make_auth_stubs(with_access_token: '')
-    Faraday::Adapter::Test::Stubs.new do |stub|
-      stub.post('/o/oauth2/token') do |env|
-        params = Addressable::URI.form_unencode(env[:body])
-        _claim, _header = JWT.decode(params.assoc('assertion').last,
-                                     @key.public_key)
-        want = ['grant_type', 'urn:ietf:params:oauth:grant-type:jwt-bearer']
-        expect(params.assoc('grant_type')).to eq(want)
-        build_json_response(
-          'access_token' => with_access_token,
-          'token_type' => 'Bearer',
-          'expires_in' => 3600
-        )
-      end
-    end
-  end
-
-  it_behaves_like 'apply/apply! are OK'
-end
diff --git a/tools/gce_setup/grpc_docker.sh b/tools/gce_setup/grpc_docker.sh
index 231625efb3a4eaeea283263845394ed243c7109d..f6b8d8c2f5cc08e3c40183b1b76ed8cc62212bb3 100755
--- a/tools/gce_setup/grpc_docker.sh
+++ b/tools/gce_setup/grpc_docker.sh
@@ -957,9 +957,10 @@ grpc_cloud_prod_auth_service_account_creds_gen_ruby_cmd() {
   local test_script="/var/local/git/grpc/src/ruby/bin/interop/interop_client.rb"
   local test_script+=" --use_tls"
   local gfe_flags=$(_grpc_prod_gfe_flags)
-  local added_gfe_flags=$(_grpc_svc_acc_test_flags)
+  local added_gfe_flags=$(_grpc_default_creds_test_flags)
   local env_prefix="SSL_CERT_FILE=/cacerts/roots.pem"
-  local the_cmd="$cmd_prefix '$env_prefix ruby $test_script $gfe_flags $added_gfe_flag $@'"
+  env_prefix+=" GOOGLE_APPLICATION_CREDENTIALS=/service_account/stubbyCloudTestingTest-7dd63462c60c.json"
+  local the_cmd="$cmd_prefix '$env_prefix ruby $test_script $gfe_flags $added_gfe_flags $@'"
   echo $the_cmd
 }
 
@@ -975,7 +976,7 @@ grpc_cloud_prod_auth_compute_engine_creds_gen_ruby_cmd() {
   local gfe_flags=$(_grpc_prod_gfe_flags)
   local added_gfe_flags=$(_grpc_gce_test_flags)
   local env_prefix="SSL_CERT_FILE=/cacerts/roots.pem"
-  local the_cmd="$cmd_prefix '$env_prefix ruby $test_script $gfe_flags $added_gfe_flag $@'"
+  local the_cmd="$cmd_prefix '$env_prefix ruby $test_script $gfe_flags $added_gfe_flags $@'"
   echo $the_cmd
 }
 
@@ -1153,6 +1154,11 @@ _grpc_svc_acc_test_flags() {
   echo " --service_account_key_file=/service_account/stubbyCloudTestingTest-7dd63462c60c.json --oauth_scope=https://www.googleapis.com/auth/xapi.zoo"
 }
 
+# default credentials test flag
+_grpc_default_creds_test_flags() {
+  echo " --oauth_scope=https://www.googleapis.com/auth/xapi.zoo"
+}
+
 # outputs the flags passed to the gcloud auth tests
 _grpc_gce_test_flags() {
   echo " --default_service_account=155450119199-r5aaqa2vqoa9g5mv2m6s3m1l293rlmel@developer.gserviceaccount.com --oauth_scope=https://www.googleapis.com/auth/xapi.zoo"