Node author can't be set when posting via HAL

Another inconsistence that I've found is that my only user (uid 1) has not uuid assigned on the users table.

That's a bug being worked on in #2050843: Users 0 and 1 are created without a UUID

From #1979260-18: Automatically populate the author default value with the current user:

I did also check several Test modules but wasn't able to find a sample where the uid was specified.

Yeah, it would be good for us to add a test for that once this support request is answered.

I can confirm that behavior:

$ curl --include --request POST --user root:root --basic --header 'Content-type: application/hal+json' http://head.local/entity/node --data-binary '{"_links":{"type":{"href":"http://head.local/rest/type/node/page"}}, "title":[{"value":"Page posted as UID 1"}], "uid":[{"target_id":"1"}]}'

Which returns:

HTTP/1.1 201 Created
Date: Fri, 20 Dec 2013 13:51:51 GMT
Server: Apache/2.4.6 (Ubuntu)
X-Powered-By: PHP/5.5.3-1ubuntu2.1
Location: http://head.local/entity/node/10
Cache-Control: must-revalidate, no-cache, post-check=0, pre-check=0, private
X-UA-Compatible: IE=edge,chrome=1
Content-language: en
Last-Modified: Fri, 20 Dec 2013 13:51:51 GMT
ETag: "1387547511"
Expires: Sun, 19 Nov 1978 05:00:00 GMT
Transfer-Encoding: chunked
Content-Type: text/html; charset=UTF-8

So, node 10 should have UID 1 as the node author but it's UID 0 (anon) instead:

mysql> SELECT nid,title,uid FROM `node_field_data` WHERE nid=10;
+-----+----------------------+-----+
| nid | title                | uid |
+-----+----------------------+-----+
|  10 | Page posted as UID 1 |   0 |
+-----+----------------------+-----+
1 row in set (0.00 sec)

I'm also unable to figure out how to set a node author via the REST API. I've attempted the same POST syntax as shown in above comments in various combinations.

Thanks for the report.
I followed your steps and this seems to be working with the patch from this issue applied: #2180109: Change the current_user service to a proxy

Just got to this issue again and I also confirm it now works fine. Thanks for the pointer @MartijnBraam!