auth.rb

require 'googleauth'
require 'googleauth/stores/file_token_store'

module SEO
  class Auth
    OOB_URI = 'urn:ietf:wg:oauth:2.0:oob'
    USER_ID_KEY = 'GOOGLE_SEARCH_CONSOLE_USER_ID'

    attr_reader :token_file, :secret, :id

    def initialize(id: ENV['GOOGLE_SEARCH_CONSOLE_CLIENT_ID'],
                   secret: ENV['GOOGLE_SEARCH_CONSOLE_CLIENT_SECRET'],
                   token_file: 'tmp/tokens.yml')
      @id = id
      @secret = secret
      @token_file = token_file
    end

    def headers
      Hash[authorize.apply({}).map { |k, v| [k.to_s, v] }]
    end

    def authorize(user_id = ENV[USER_ID_KEY])
      creds = authorizer.get_credentials(user_id)

      if creds.nil?
        launch_browser(user_id)
      else
        creds
      end
    end

    def authorize!(user_id = ENV[USER_ID_KEY])
      launch_browser(user_id)
    end

    private

    def launch_browser(user_id)
      url = authorizer.get_authorization_url(base_url: OOB_URI)
      puts "Open #{url} in your browser and enter the resulting code:"
      code = STDIN.gets
      authorizer.get_and_store_credentials_from_code(user_id: user_id, code: code, base_url: OOB_URI)
    end

    def scopes
      %w(https://www.googleapis.com/auth/webmasters)
    end

    def authorizer
      @authorized ||= Google::Auth::UserAuthorizer.new(client_id, scopes, token_store)
    end

    def client_id
      Google::Auth::ClientId.new(id, secret)
    end

    def token_store
      @token_store ||= Google::Auth::Stores::FileTokenStore.new(file: token_file)
    end
  end
end

Simple class to get access to Google APIs in a command line interface tools.

Set environment variables for user_id (probably your email), client_id and client_secret (found in google api console), then you can use the api:

authorize! forces a new login.
authorize tries to use existing login
headers returns a properly formatted header, can be dropped right into your request function