Add all headers to cache key by default

[ofhouse]

Currently, no headers are part of the cache key.
This is generally better for caching but when people use Authorization headers this could cause a security risk.

So the ideal behaviour would be a caching based on all headers that can be configured through input variables.

https://github.com/dealmore/terraform-aws-next-js/blob/30cc0bff5c330ed59fa071d3f9ba35a7cf72eb82/modules/proxy/main.tf#L119

Blocked by hashicorp/terraform-provider-aws#14373.

[ofhouse]

To resolve the issue the default_cache_behavior needs to add headers to forwarded_values:

 forwarded_values {
      query_string = true
+     headers      = var.cloudfront_cache_headers

      cookies {
        forward = "all"
      }
    }

Unfortunately, headers property cannot be set on S3 origin resources.

A possible solution would be to set the API Gateway origin as default origin, but then we lose the ability to use origin access identity: https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/lambda-event-structure.html

• You can’t use an OAI when you change the request from a custom origin to an Amazon S3 origin.

So we have to wait until we can use the origin request policies to add headers to the S3 origin, which should be possible.