Generate GCP tokens through cmd-path config

This commit pushes the `Kubeclient::GoogleApplicationDefaultCredentials`
implementation down to a `GCPAuthProvider` that handle both code paths of
how to generate GCP tokens.

kubeclient.gemspec

@@ -30,6 +30,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'googleauth', '~> 0.5.1'
   spec.add_development_dependency('mocha', '~> 1.5')
   spec.add_development_dependency 'openid_connect', '~> 1.1'
+  spec.add_development_dependency 'jsonpath', '~> 1.0'
 
   spec.add_dependency 'rest-client', '~> 2.0'
   spec.add_dependency 'recursive-open-struct', '~> 1.0', '>= 1.0.4'

lib/kubeclient.rb

@@ -4,8 +4,8 @@
 require 'kubeclient/common'
 require 'kubeclient/config'
 require 'kubeclient/entity_list'
-require 'kubeclient/google_application_default_credentials'
 require 'kubeclient/exec_credentials'
+require 'kubeclient/gcp_auth_provider'
 require 'kubeclient/http_error'
 require 'kubeclient/missing_kind_compatibility'
 require 'kubeclient/oidc_auth_provider'

lib/kubeclient/config.rb

@@ -150,23 +150,33 @@ def fetch_user_auth_options(user)
       if user.key?('token')
         options[:bearer_token] = user['token']
       elsif user.key?('exec')
-        exec_opts = user['exec'].dup
-        exec_opts['command'] = ext_command_path(exec_opts['command']) if exec_opts['command']
+        exec_opts = expand_command_option(user['exec'], 'command')
         options[:bearer_token] = Kubeclient::ExecCredentials.token(exec_opts)
       elsif user.key?('auth-provider')
-        auth_provider = user['auth-provider']
-        options[:bearer_token] = case auth_provider['name']
-                                 when 'gcp'
-                                 then Kubeclient::GoogleApplicationDefaultCredentials.token
-                                 when 'oidc'
-                                 then Kubeclient::OIDCAuthProvider.token(auth_provider['config'])
-                                 end
+        options[:bearer_token] = fetch_token_from_provider(user['auth-provider'])
       else
         %w[username password].each do |attr|
           options[attr.to_sym] = user[attr] if user.key?(attr)
         end
       end
       options
     end
+
+    def fetch_token_from_provider(auth_provider)
+      case auth_provider['name']
+      when 'gcp'
+        config = expand_command_option(auth_provider['config'], 'cmd-path')
+        Kubeclient::GCPAuthProvider.token(config)
+      when 'oidc'
+        Kubeclient::OIDCAuthProvider.token(auth_provider['config'])
+      end
+    end
+
+    def expand_command_option(config, key)
+      config = config.dup
+      config[key] = ext_command_path(config[key]) if config[key]
+
+      config
+    end
   end
 end

lib/kubeclient/gcp_auth_provider.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require 'kubeclient/google_application_default_credentials'
+require 'kubeclient/gcp_command_credentials'
+
+module Kubeclient
+  # Handle different ways to get a bearer token for Google Cloud Platform.
+  class GCPAuthProvider
+    class << self
+      def token(config)
+        if config.key?('cmd-path')
+          Kubeclient::GCPCommandCredentials.token(config)
+        else
+          Kubeclient::GoogleApplicationDefaultCredentials.token
+        end
+      end
+    end
+  end
+end

lib/kubeclient/gcp_command_credentials.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+module Kubeclient
+  # Generates a bearer token for Google Cloud Platform.
+  class GCPCommandCredentials
+    class << self
+      def token(config)
+        require 'open3'
+        require 'shellwords'
+        require 'json'
+        require 'jsonpath'
+
+        cmd = config['cmd-path']
+        args = config['cmd-args']
+        token_key = config['token-key']
+
+        out, err, st = Open3.capture3(cmd, *args.split(' '))
+
+        raise "exec command failed: #{err}" unless st.success?
+
+        extract_token(out, token_key)
+      end
+
+      private
+
+      def extract_token(output, token_key)
+        JsonPath.on(output, token_key.gsub(/^{|}$/, '')).first
+      end
+    end
+  end
+end

test/config/gcpcmdauth.kubeconfig

@@ -0,0 +1,26 @@
+apiVersion: v1
+clusters:
+- cluster:
+    server: https://localhost:8443
+    insecure-skip-tls-verify: true
+  name: localhost:8443
+contexts:
+- context:
+    cluster: localhost:8443
+    namespace: default
+    user: application-default-credentials
+  name: localhost/application-default-credentials
+kind: Config
+preferences: {}
+users:
+- name: application-default-credentials
+  user:
+    auth-provider:
+      config:
+        access-token: <fake_token>
+        cmd-args: config config-helper --format=json
+        cmd-path: /path/to/gcloud
+        expiry: 2019-04-09T19:26:18Z
+        expiry-key: '{.credential.token_expiry}'
+        token-key: '{.credential.access_token}'
+      name: gcp

test/test_config.rb

@@ -146,6 +146,20 @@ def test_gcp_default_auth_renew
     assert_equal({ bearer_token: 'token1' }, context.auth_options)
   end
 
+  def test_gcp_command_auth
+    Kubeclient::GCPCommandCredentials.expects(:token)
+                                     .with('access-token' => '<fake_token>',
+                                           'cmd-args' => 'config config-helper --format=json',
+                                           'cmd-path' => '/path/to/gcloud',
+                                           'expiry' => '2019-04-09 19:26:18 UTC',
+                                           'expiry-key' => '{.credential.token_expiry}',
+                                           'token-key' => '{.credential.access_token}')
+                                     .returns('token1')
+                                     .once
+    config = Kubeclient::Config.read(config_file('gcpcmdauth.kubeconfig'))
+    config.context(config.contexts.first)
+  end
+
   def test_oidc_auth_provider
     Kubeclient::OIDCAuthProvider.expects(:token)
                                 .with('client-id' => 'fake-client-id',

test/test_gcp_command_credentials.rb

@@ -0,0 +1,27 @@
+require_relative 'test_helper'
+require 'open3'
+
+# Unit tests for the GCPCommandCredentials token provider
+class GCPCommandCredentialsTest < MiniTest::Test
+  def test_token
+    opts = { 'cmd-args' => 'config config-helper --format=json',
+             'cmd-path' => '/path/to/gcloud',
+             'expiry-key' => '{.credential.token_expiry}',
+             'token-key' => '{.credential.access_token}' }
+
+    creds = JSON.dump(
+      'credential' => {
+        'access_token' => '9A3A941836F2458175BE18AA1971EBBF47949B07',
+        'token_expiry' => '2019-04-12T15:02:51Z'
+      }
+    )
+
+    st = Minitest::Mock.new
+    st.expect(:success?, true)
+
+    Open3.stub(:capture3, [creds, nil, st]) do
+      assert_equal('9A3A941836F2458175BE18AA1971EBBF47949B07',
+                   Kubeclient::GCPCommandCredentials.token(opts))
+    end
+  end
+end