D8 Port: Service endpoint integration

@canutza: When I tested the web services integration locally, I was able to register a token for an anonymous user (user = 0), so I'll mark this item as done in the list without a code change.

Agreed on the error messages. They might not be pretty, but the HTTP status codes should be enough. Let's stick with Drupal provides out of the box.

Regarding canonical URLs: I'd like to move the canonical URL of the push notifications token from /admin/config/services/push_notifications/token to /push_notifications/token. I'll give it a try and will see if I can also figure out the issue why the canonical URL does not work to create a new token.

I've changed the canonical URL for token entities to be /push_notifications/token/{push_notifications_token}. I've marked both pages as admin pages in the routing configuration.

I've looked into the issue about creating a new entity over REST vs. deleting it or getting it, and using different URLs. This URL gives a pretty good overview for how this is being done in JavaScript for nodes, users, and terms: https://www.drupal.org/documentation/modules/rest/javascript. It seems that for nodes, the same issue exists. In order to create a new node, the endpoint is http://example.com/entity/node, whereas to GET the node, the endpoint is http://example.com/node/123?_format=json.

This article https://www.drupal.org/documentation/modules/rest/post seems to indicate that starting in Drupal 8.2.0, new nodes can be created without the entity component in the path. I wonder if that will be the same for any entity, but I haven't tried Drupal 8.2.0 yet.

Examples for REST integration

Here are the examples that I used to POST tokens, GET tokens, and DELETE tokens. My example site lives at local.sd8.com and I'm using Basic Authorization, which is converted into a hash. The tool I used to play around was Postman. All the examples are HTTP request examples.

POST

POST /entity/push_notifications_token HTTP/1.1
Host: local.sd8.com
X-CSRF-Token: ivTNJtmq8z_qAIW-P9uvIFJZrTggQfokWX13lM6-cy0
Content-Type: application/json
Authorization: Basic bWFyaW86dGVzdGVy
Cache-Control: no-cache

{
  "token": [
    {
      "value": "123ab312123"
    }
  ],
  "network": [
    {
      "value": "gcm"
    }
  ]
}

=> Status Code 201

GET

GET /push_notifications/token/18?_format=json HTTP/1.1
Host: local.sd8.com
X-CSRF-Token: ivTNJtmq8z_qAIW-P9uvIFJZrTggQfokWX13lM6-cy0
Content-Type: application/json
Authorization: Basic bWFyaW86dGVzdGVy
Cache-Control: no-cache

=> Status Code 200

DELETE

GET /push_notifications/token/18?_format=json HTTP/1.1
Host: local.sd8.com
X-CSRF-Token: ivTNJtmq8z_qAIW-P9uvIFJZrTggQfokWX13lM6-cy0
Content-Type: application/json
Authorization: Basic bWFyaW86dGVzdGVy
Cache-Control: no-cache

=> Status Code 204

I think this is ready for review.

@canutza: Thanks for retrying. I just tried registering a token for an anonymous user again and was able to do so with the latest 8.x-1.x dev branch. The only thing I needed was a valid CSFR token. I've attached my permissions and here's the code I used to register the token:

POST /entity/push_notifications_token HTTP/1.1
Host: local.sd8.com
Content-Type: application/json
X-CSRF-Token: x0L8NnHQGJJp79zYZlmAqy2p1rCTQBWr4wytsP_fKWY
Cache-Control: no-cache
Postman-Token: 0a1c3adb-1d57-7ade-521d-4cfa5775e12f

{
  "token": [
    {
      "value": "123abza312123"
    }
  ],
  "network": [
    {
      "value": "gcm"
    }
  ]
}