def add_credential(rack_env, type, credential)
      Env.new(rack_env).tap do |env|
        env.credentials[type] = credential
      end.to_rack
    end
def add_credential(rack_env, type, credential)
      Env.new(rack_env).tap do |env|
        env.credentials[type] = credential
      end.to_rack
    end
Add a credential to the Rack environment

 @param [Hash] :rack_env Rack environment
 @param [String] :type credential type to add to the environment
 @param [Object] :credential object to add to the environment