anchor.diff:  + `http` : It is used to convey parameters for providers which deliver information through the HTTP protocol.
   (Only protocol supported nowadays).
   It must contain a subfield named `url` with the URL that serves as the endpoint that offers the providing interface.
  -The endpooint must *not* include the protocol
  +The endpoint must *not* include the protocol
   specific part (for instance `/v2/entities`). 
  -+ `legacy` : `true` if this provider only supports NGSIv1 protocol. `false` if this provider supports NGSIv2.
  -Currently `true` by default. In the future, will be changed to `false`. 
   + `supportedForwardingMode` : It is used to convey the forwarding mode supported by this context provider. By default `all`. 
   Allowed values are:
       + `none` : This provider does not support request forwarding.
  
positive.code: 
  # Group Registrations
  
  A Context Registration allows to bind external context information sources so that they can be
  play the role of providers
  of certain subsets (entities, attributes) of the context information space, including those located
  at specific geographical areas.
  A compliant Context Information provider shall expose an NGSI10 (legacy) or an NGSIv2 interface, in particular:
  
  * Query by entity type(s), entity id(s), geoquery and attribute and/or metadata projection
  (`attrs` or `metadata` parameter). (See `GET /v2/entities`)
  
negative.code:             },
              "provider": {
                "http": {
                  "url": "http://contextsource.example.org"
                },
                "supportedForwardingMode": "all"
              },
              "expires": "2017-10-31T12:00:00",
              "status": "active",
              "forwardingInformation": {
                "timesSent": 12,
                "lastForwarding": "2017-10-06T16:00:00.00Z",
                "lastSuccess": "2017-10-06T16:00:00.00Z",
                "lastFailure": "2017-10-05T16:00:00.00Z"
              }
            }
          ]
  