Request Signing

Protocol

All requests which modify the database must be signed. Signing is performed by a pre-shared key between the sender and RCS using the following procedure

SIGNATURE := hmac_sha256( MSG, KEY )
MSG := concat( REQUEST_PATH, SENDER_ID, TIME_STAMP, REQUEST_BODY )
REQUEST_PATH := <the request path including opening '/' as defined in RFC 2396>
SENDER_ID := <pre-shared identifier with RCS>
TIME_STAMP := <ISO 8601 date and time in UTC time zone>
REQUEST_BODY := JSON fragment | ""

Once the signature has been computed it should be encoded in modified base64 ( http://tools.ietf.org/html/rfc4648#section-5 ) with any padding = characters stripped from the end. The encoded signature should be attached to the HTTP request along with the following custom HTTP headers

Authorization: <signature as encoded above>
TimeStamp: <ISO 8601 date and time, must match the exact text used for signing>
Sender: <pre-shared identifier with RCS>

Once computed, the signature is considered valid for +/- 2 minutes of the time for which it was computed (to account for any potential clock skew between the systems).

Example

Here’s a walkthrough of a possible interaction between GeoCat and RCS. The sample computations are valid and can be used for testing if a client is unavailable.

1. GeoCat and RCS team pre-share a private key and a client identifier.

2. RCS stores a mapping between the key and the client id (GeoCat).

3. GeoCat generates REST request for registering a layer in RCS.

   URL

   PUT http://rcs.example.com/register/23ax5t

   Payload

   {"version":"1.0.0","payload_type":"wms","en":{"service_url":"http://wms.ess-ws.nrcan.gc.ca/wms/toporama_en","layer":"limits"},"fr":{"service_url":"http://wms.ess-ws.nrcan.gc.ca/wms/toporama_en","layer":"limits"}}
   

   Request time

   2014-12-05T18:28:56.714Z

   Sender ID

   jstest

4. GeoCat computes the message string by concatenating the fragments specified in the Protocol section

   REQUEST_PATH = /register/23ax5t
   SENDER_ID = jstest
   TIME_STAMP = 2014-12-05T18:28:56.714Z
   REQUEST_BODY =  {"version":"1.0.0","payload_type":"wms","en":{"service_url":"http://wms.ess-ws.nrcan.gc.ca/wms/toporama_en","layer":"limits"},"fr":{"service_url":"http://wms.ess-ws.nrcan.gc.ca/wms/toporama_en","layer":"limits"}}
   

   resulting in

   MSG = /register/23ax5tjstest2014-12-05T18:28:56.714Z{"version":"1.0.0","payload_type":"wms","en":{"service_url":"http://wms.ess-ws.nrcan.gc.ca/wms/toporama_en","layer":"limits"},"fr":{"service_url":"http://wms.ess-ws.nrcan.gc.ca/wms/toporama_en","layer":"limits"}}
   

5. GeoCat generates the authorization code using the method described in Protocol

   SIGNATURE = hmac_sha256( <MSG as above>, 'test_-k' )
             = 0xbfa5da41ab32673726fc1cf85bfa797ced706f224a0999c9144b29217c3d7a56
   

6. GeoCat encodes the HMAC digest in modified base64

   ENCODED_SIGNATURE = base64_encode( HMAC_DIGEST ).replace('+','-').replace('/','_').replace('=','')
                     = v6XaQasyZzcm_Bz4W_p5fO1wbyJKCZnJFEspIXw9elY
   

7. GeoCat appends the HTTP headers

   "Authorization: v6XaQasyZzcm_Bz4W_p5fO1wbyJKCZnJFEspIXw9elY"
   "TimeStamp: 2014-12-05T18:28:56.714Z"
   "Sender: jstest"
   

   and sends the request (sample request escaped for the Windows command prompt)

   curl -X PUT http://localhost:5000/register/23ax5t
       -H "Authorization: v6XaQasyZzcm_Bz4W_p5fO1wbyJKCZnJFEspIXw9elY"
       -H "TimeStamp: 2014-12-05T18:28:56.714Z"
       -H "Sender: jstest"
       -H "Content-Type: application/json"
       -d {\"version\":\"1.0.0\",\"payload_type\":\"wms\",\"en\":{\"service_url\":\"http://wms.ess-ws.nrcan.gc.ca/wms/toporama_en\",\"layer\":\"limits\"},\"fr\":{\"service_url\":\"http://wms.ess-ws.nrcan.gc.ca/wms/toporama_en\",\"layer\":\"limits\"}}
   

8. RCS receives the request

9. RCS fetches the pre-shared key from the request

   KEY = db_lookup('jstest')
       = 'test_-k'
   

10. RCS performs the same signature compuation as GeoCat, generating a reference signature

11. RCS tests that the reference signature matches the signature in the Authorization header

12. RCS verifies that the time of request is valid

    assert( -2 min < UTC_NOW - TIME_STAMP < 2 min )
    

13. RCS executes the request alternate: if the verification fails then a 401 error is sent back)