Avoids redundant class method definition (#107)

- adds module to provide `read_json_key` class method
    to multiple classes

lib/googleauth/json_key_reader.rb

@@ -0,0 +1,45 @@
+# 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.
+
+module Google
+  # Module Auth provides classes that provide Google-specific authorization
+  # used to access Google APIs.
+  module Auth
+    # JsonKeyReader contains the behaviour used to read private key and
+    # client email fields from the service account
+    module JsonKeyReader
+      def read_json_key(json_key_io)
+        json_key = MultiJson.load(json_key_io.read)
+        raise 'missing client_email' unless json_key.key?('client_email')
+        raise 'missing private_key' unless json_key.key?('private_key')
+        [json_key['private_key'], json_key['client_email']]
+      end
+    end
+  end
+end

lib/googleauth/service_account.rb

@@ -29,6 +29,7 @@
 
 require 'googleauth/signet'
 require 'googleauth/credentials_loader'
+require 'googleauth/json_key_reader'
 require 'jwt'
 require 'multi_json'
 require 'stringio'
@@ -48,6 +49,7 @@ module Google
     class ServiceAccountCredentials < Signet::OAuth2::Client
       TOKEN_CRED_URI = 'https://www.googleapis.com/oauth2/v4/token'.freeze
       extend CredentialsLoader
+      extend JsonKeyReader
 
       # Creates a ServiceAccountCredentials.
       #
@@ -69,15 +71,6 @@ module Google
             signing_key: OpenSSL::PKey::RSA.new(private_key))
       end
 
-      # Reads the private key and client email fields from the service account
-      # JSON key.
-      def self.read_json_key(json_key_io)
-        json_key = MultiJson.load(json_key_io.read)
-        raise 'missing client_email' unless json_key.key?('client_email')
-        raise 'missing private_key' unless json_key.key?('private_key')
-        [json_key['private_key'], json_key['client_email']]
-      end
-
       # Handles certain escape sequences that sometimes appear in input.
       # Specifically, interprets the "\n" sequence for newline, and removes
       # enclosing quotes.
@@ -132,6 +125,7 @@ module Google
       SIGNING_ALGORITHM = 'RS256'.freeze
       EXPIRY = 60
       extend CredentialsLoader
+      extend JsonKeyReader
 
       # make_creds proxies the construction of a credentials instance
       #
@@ -144,15 +138,6 @@ module Google
         new(json_key_io: args[0][:json_key_io])
       end
 
-      # Reads the private key and client email fields from the service account
-      # JSON key.
-      def self.read_json_key(json_key_io)
-        json_key = MultiJson.load(json_key_io.read)
-        raise 'missing client_email' unless json_key.key?('client_email')
-        raise 'missing private_key' unless json_key.key?('private_key')
-        [json_key['private_key'], json_key['client_email']]
-      end
-
       # Initializes a ServiceAccountJwtHeaderCredentials.
       #
       # @param json_key_io [IO] an IO from which the JSON key can be read