instance method call

# File actionpack/lib/action_dispatch/http/content_security_policy.rb, line 17
      def call(env)
        request = ActionDispatch::Request.new env
        _, headers, _ = response = @app.call(env)

        return response if policy_present?(headers)

        if policy = request.content_security_policy
          nonce = request.content_security_policy_nonce
          nonce_directives = request.content_security_policy_nonce_directives
          context = request.controller_instance || request
          headers[header_name(request)] = policy.build(context, nonce, nonce_directives)
        end

        response
      end