What is the format expected by a find(id) request? - ember.js

Question

My backend replies to find all requests:
User.find();
Like this
{ 'users' : [ user1_obj, user2_obj ] }
Ember-data is happy about it. Now if I do a simple single object find:
User.find('user1');
I have tried configuring the backend to return any of the following:
user1
{ 'user1' : user1_obj }
{ 'user' : { 'user1' : user1_obj } }
{ 'user' : user1_obj }
But none of those are working. What should I return from the backend in reply to find("obj-id") requests? According to the documentation about JSON ROOT, the right format looks like:
{ 'user' : user1_obj }
Ember does not complain about it, but the Ember Objects processed have a very strange structure, like this:
As you can see, _reference.record is referring to the top record. Also (not shown here) _data field is empty.
What could be causing that strange nesting?
EDIT
As linked by mavilein in his answer, the JSON API suggests using a different format for singular resources:
{ 'users' : [user1_obj] }
That means, the same format as for plural resources. Not sure if Ember will swallow that, I'll check now.

Answer 1

Following this specification, i would suspect the following:
{
'users' : [{
"id": "1",
"name" : "John Doe"
},{
"id": "2",
"name" : "Jane Doe"
}]
}
For singular resources the specification says:
Singular resources are represented as JSON objects. However, they are
still wrapped inside an array:
{
'users' : [{
"id": "1",
"name" : "John Doe"
}]
}

Answer 2

Using User.find() will expect the rootKey pluralized and in your content an array of elements, the response format is the following json:
{
users: [
{ id: 1, name: 'Kris' },
{ id: 2, name: 'Luke' },
{ id: 3, name: 'Formerly Alex' }
]
}
And with User.find(1) the rootKey in singular, and just one object:
{
user: {
id: 1, name: 'Kris'
}
}
Here a demo showing this working