# Bug Report

# Detailed description
This is a similar issue to #2329, specific to [S3 Presigned URLs](https://boto3.amazonaws.com/v1/documentation/api/latest/guide/s3-presigned-urls.html). Using the edge router port (`:4566`), it is possible to use `generate_presigned_post`, but attempting to use the resultant URL to upload a file to localstack's S3 fails with a 404.

## Expected behavior
Localstack's edge router port should accept POST requests with an S3 Presigned URL (generated from that same Localstack instance) in the same way that the old S3 port (`:4572`) does.

## Actual behavior
While the old S3 port (`:4572`) handles this fine, the edge router responds with a 404 and a message similar to the following:

```
2020-05-24T15:36:54:INFO:localstack.services.edge: Unable to find forwarding rule for host "localhost:4566", path "/local-job-documents", target header "", auth header ""
```

(borrowed from @philippmalkov's comment on #2329 )

```
aws_1  | 2020-05-27T16:24:38:INFO:localstack.services.edge: Unable to find forwarding rule for host "aws:4566", path "/test-bucket", target header "", auth header ""
```

(our observed case with the below setup)

# Steps to reproduce

## Command used to start LocalStack
```
# Used in docker-compose.yml as:
  aws:
    image: localstack/localstack-light
    environment:
      - SERVICES=dynamodb,s3
      - HOSTNAME_EXTERNAL=aws
      - DEBUG=1
      - DATA_DIR=/tmp/localstack/data
    expose:
      - 4566
      - 4572
    volumes:
      - ./.localstack:/tmp/localstack
```

## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)
Client code is a Django app using `boto3` to generate a Presigned URL and then upload a file to it using `requests`, effectively identical to the examples in [the boto3 docs](https://boto3.amazonaws.com/v1/documentation/api/latest/guide/s3-presigned-urls.html)
auth_header = headers.get('authorization', '')
        host = headers.get('host', '')
        headers[HEADER_LOCALSTACK_EDGE_URL] = 'https://%s' % host
        
        api, port, path, host = get_api_from_headers(headers, path)
        if port and int(port) < 0:
            return 404
        if not port:
            port = get_port_from_custom_rules(method, path, data, headers) or port
        if not port:
            if api in ['', None, '_unknown_']:
                LOG.info(('Unable to find forwarding rule for host "%s", path "%s", '
                    'target header "%s", auth header "%s"') % (host, path, target, auth_header))
            else:
                LOG.info(('Unable to determine forwarding port for API "%s" - please '
                    'make sure this API is enabled via the SERVICES configuration') % api)
            response = Response()
            response.status_code = 404
            response._content = '{"status": "running"}'
            return response
        use_ssl = config.USE_SSL
        connect_host = '%s:%s' % (config.HOSTNAME, port)
        url = 'http%s://%s%s' % ('s' if use_ssl else '', connect_host, path)
        headers['Host'] = host
        function = getattr(requests, method.lower())
        if isinstance(data, dict):
            data = json.dumps(data)
        response = function(url, data=data, headers=headers, verify=False)
        return response
def get_api_from_headers(headers, path=None):