Getting raw event.body from API Gateway when specifying a JSON schema

I configured a JSON schema for an http endpoint and no longer receive the raw request string in event.body but instead receive a parsed object. This would normally be convenient to have a validated object, but the requests are signed with an HMAC signature which cannot be validated without the original request body. Is it possible to have both?

events: [
  {
    http: {
      method: 'post',
      path: 'shopifyOrder',
      request: {
        schema: {
          'application/json': schema
        }
      }
    }
  }
]

Update: I have a workaround using httpApi instead of http, which does no schema validation but returns the original payload. I am still looking for a solution that validates it up front and delivers the original string.