Network Working Group M. Jones
Internet-Draft Y. Goland
Intended status: Standards Track Microsoft
Expires: January 7, 2013 July 6, 2012
Simple Web Discovery (SWD)
draft-jones-simple-web-discovery-03
Abstract
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.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . . 3
2. Simple Web Discovery Request . . . . . . . . . . . . . . . . . 3
3. Simple Web Discovery Responses . . . . . . . . . . . . . . . . 4
3.1. Response Containing One or More Locations . . . . . . . . 4
3.2. Redirecting All Simple Web Discovery Requests . . . . . . 5
3.3. 401 Unauthorized Response . . . . . . . . . . . . . . . . 7
3.4. Other HTTP 1.1 Responses . . . . . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . . 9
Appendix A. Document History . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
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%3Aexamp
le%3Aservice%3Acalendar".
1.1. Notational Conventions
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].
2. Simple Web Discovery Request
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.
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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.
3. Simple Web Discovery Responses
3.1. Response Containing One or More Locations
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.
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3.2. Redirecting All Simple Web Discovery Requests
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):
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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.
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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.
3.3. 401 Unauthorized Response
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].
3.4. Other HTTP 1.1 Responses
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.
4. IANA Considerations
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]:
URI suffix: simple-web-discovery
Change controller: IETF
Specification document: [[ this document ]]
5. Security Considerations
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
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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.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the
Internet: Timestamps", RFC 3339, July 2002.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785,
April 2010.
[W3C.REC-html401-19991224]
Hors, A., Raggett, D., and I. Jacobs, "HTML 4.01
Specification", World Wide Web Consortium
Recommendation REC-html401-19991224, December 1999,
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<http://www.w3.org/TR/1999/REC-html401-19991224>.
6.2. Informative References
[JWT] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", July 2012.
Appendix A. Document History
[[ to be removed by the RFC editor before publication as an RFC ]]
-03
o Changed "requests use the x-www-form-urlencoded format" to
"requests use query parameters" and changed "an x-www-form-
urlencoded form" to "a form encoded using the application/
x-www-form-urlencoded encoding algorithm", both at the suggestion
of Julian Reschke. x-www
o Updated examples to use "urn:example:" URNs rather than
"urn:example.org:" URNs, also at Julian's suggestion.
o Applied applicable editorial improvements from JOSE specs to SWD.
o Updated references to related specifications.
-02
o Update examples to use example.{com,net,org} domain names.
o Provide encoded representation of the request-URI query parameters
for the first example request.
o Changed "200 O.K." to "200 OK".
o Respect line length restrictions in examples.
o No normative changes.
-01
o Refresh draft before expiration of -00. No normative changes.
-00
o Initial version.
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Authors' Addresses
Michael B. Jones
Microsoft
Email: mbj@microsoft.com
URI: http://self-issued.info/
Yaron Y. Goland
Microsoft
Email: yarong@microsoft.com
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