src/ruby/lib/grpc/auth/compute_engine.rb

# Copyright 2015, Google Inc.
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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