| Network Working Group | M.B. Jones |
| Internet-Draft | Y.Y. Goland |
| Intended status: Standards Track | Microsoft |
| Expires: January 05, 2013 | July 6, 2012 |
Simple Web Discovery (SWD)
draft-jones-simple-web-discovery-03
Simple Web Discovery (SWD) defines an HTTPS GET based mechanism to discover the location of a given type of service for a given principal starting only with a domain name.
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Simple Web Discovery (SWD) defines an HTTPS GET based mechanism to discover the location of a given type of service for a given principal starting only with a domain name. SWD requests use query parameters to specify a URI for the principal and another URI for the type of service being sought. If the request is successful then the response, by default, is a JavaScript Object Notation (JSON) [RFC4627] object containing an array of URIs that point to where the principal has instances of services of the requested type.
For example, let us say that a requester wants to discover where Joe keeps his calendar. The requester could take Joe's e-mail address, joe@example.com, and use its domain to create an HTTPS GET request of the following form (with long lines broken for display purposes only):
GET /.well-known/simple-web-discovery
?principal=mailto:joe@example.com
&service=urn:example:service:calendar HTTP/1.1
Host: example.com
HTTP/1.1 200 OK
Content-Type: application/json
{
"locations": ["https://calendars.example.net/calendars/joseph"]
}
Note: The request-URI is left unencoded in the above example for the sake of readability. The query parameters above would actually be encoded as ?principal=mailto%3Ajoe%40example.com&service=urn%3Aexample%3Aservice%3Acalendar.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in Key words for use in RFCs to Indicate Requirement Levels [RFC2119].
Domains that support SWD requests MUST make available a SWD server for their domain at the path /.well-known/simple-web-discovery. The syntax and semantics of /.well-known are defined in RFC 5785 [RFC5785]. simple-web-discovery MUST point to a SWD server compliant with this specification.
SWD servers MUST support receiving SWD requests via TLS 1.2 [RFC5246] and MAY support other transport layer security mechanisms of equivalent security. SWD servers MUST reject SWD requests sent over plain HTTP or any other transport that does not provide both privacy and validation of the server's identity.
A SWD server is queried using an HTTPS GET request with the previously specified path along with a query segment containing a form encoded using the application/x-www-form-urlencoded encoding algorithm as defined in HTML 4.01 [W3C.REC-html401-19991224]. The form MUST contain two name/value pairs that MUST appear exactly once, principal and service. Both name/value pairs MUST have values that are set to URIs [RFC3986]. If any of the previous requirements are not met in a SWD request, then the request MUST be rejected with a 400 Bad Request.
The SWD request form MAY contain additional name/value pairs but if those name/value pairs are not recognized by the SWD server then the SWD server MUST ignore them for processing purposes.
The principal query component is a URI that identifies an entity. The service query component is a URI that identifies a service type. The semantics of the SWD query is "Please return the location(s) of instances of the specified service type associated with the specified principal". The definition of URIs used to identify principals and services are outside the scope of this specification.
Unless another content-type is negotiated, a 200 OK response to a SWD request that contains the information requested MUST return content of type application/json [RFC4627]. The JSON response MUST contain a JSON object that contains a member pair whose name is the string locations and whose value is an array of strings that are each a URI pointing to a location where the desired service type belonging to the specified principal can be found. There are no semantics associated with the order in which the URIs are listed in the array.
The JSON object MAY contain other members but a receiver of the object MAY ignore any member pairs whose name it does not recognize.
SWD requests by definition start off by being issued to the /.well-known/simple-web-discovery location. But locating a SWD server at a root location can prove inconvenient. To enable service level redirection, a SWD server MAY return a 200 OK to an HTTPS request with a content type of application/json (or whatever other content type has been negotiated) that contains a JSON object that contains a member pair whose name is the string SWD_service_redirect whose value is a JSON object with a member pair whose name is location and whose value is a string that encodes a URI. Optionally, the JSON object value of SWD_service_redirect MAY also contain a member whose name is expires and whose value is a JSON number that encodes an integer.
A SWD compliant client MUST support the SWD_service_redirect response.
The JSON objects MAY contain other members but a receiver of the objects MAY ignore any pairs whose name it does not recognize.
The location member identifies the URI that the caller MUST redirect all SWD requests for that domain to until the expires time has passed. SWD requests for the redirected domain MUST be constructed by taking the URI returned in the location and using it as the base URI to which the SWD form arguments are then added as query parameters. The location URI MUST NOT include a query component.
The following is an example of redirect messages (with long lines broken for display purposes only):
GET /.well-known/simple-web-discovery
?principal=mailto:joe@example.com
&service=urn:example:service:calendar HTTP/1.1
Host: example.com
HTTP/1.1 200 OK
Content-Type: application/json
{
"SWD_service_redirect":
{
"location": "https://swd.example.com/swd_server",
"expires": 1300752001
}
}
GET /swd_server
?principal=mailto:joe@example.com
&service=urn:example:service:calendar HTTP/1.1
Host: swd.example.com
HTTP/1.1 200 OK
Content-Type: application/json
{
"locations": ["https://calendars.example.net/calendars/joseph"]
}
Note: The request-URIs are left unencoded in the above example for the sake of readability.
The location URI MUST be an HTTPS URL.
The optional expires member identifies the point in time at which the caller MUST NOT redirect its SWD requests for that domain to the previously obtained location and MUST instead return to the /.well-known/simple-web-discovery location. The value of the expires member MUST encode the number of seconds from 1970-01-01T0:0:0Z as measured in UTC until the desired date/time. See RFC 3339 [RFC3339] for details regarding date/times in general and UTC in particular. If the expires value is in the past or if the value is more than one hour in the future then the response MUST be treated as if it didn't contain an expires value.
If the expires value is omitted or if its value is incorrect then the expires value MUST be treated as having a value of exactly one hour into the future.
If a JSON response is received that contains both a member pair with the name SWD_service_redirect and a member pair with the name locations as children of the object root then the SWD_service_redirect member pair MUST be ignored.
A SWD server MAY respond to a request with a 401 Unauthorized Response, as described in RFC 2616 [RFC2616], Section 10. Per the RFC, the request MAY be repeated with a suitable Authorization header field. Authorization information may be communicated in this manner, including a JSON Web Token [JWT].
A SWD server MAY return other HTTP 1.1 responses, including 404 Not Found, 400 Bad Request, and 403 Forbidden. SWD implementations MUST correctly handle these responses.
This specification registers a well-known URI suffix value relative to "/.well-known/" in the IANA Well-Known URI registry defined in RFC 5785 [RFC5785]:
SWD responses can contain confidential information. Therefore a, general approach is used to require TLS in all cases. But TLS can only provide for privacy and server validation, it cannot validate that the requester is authorized to see the results of a query. The exact mechanism used to determine if the requester is authorized to see the result of the query is outside the scope of this specification.
Because SWD responses can contain confidential information, the requestor may need authorization to receive them. Standard HTTP authorization mechanisms MAY be employed to request authorized access, including the use of an HTTP Authorization header field in requests, which in turn, may contain a JSON Web Token [JWT], among other authorization data formats.
The ability to redirect an entire SWD server as defined in this document is an obvious attack point. This is another reason why we have mandated TLS, so as to be sure that the redirect can only be received over a secure connection. We have also put in the upper limit of 60 minutes for a redirect so as to provide a path for regaining control over queries should a successful attack be launched to return false redirects.
The SWD_service_redirect capability may cause unanticipated failures in cases where a requestor may have permissions to discover content at the original SWD endpoint but not the one redirected to, or vice-versa.
| [JWT] | Jones, M.B., Bradley, J. and N. Sakimura, "JSON Web Token (JWT)", July 2012. |
[[ to be removed by the RFC editor before publication as an RFC ]]
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