WebFinger
draft-ietf-appsawg-webfinger-07
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (appsawg WG) | |
|---|---|---|---|
| Authors | Paul Jones , Gonzalo Salgueiro , Joseph Smarr | ||
| Last updated | 2012-12-02 | ||
| Replaces | draft-jones-appsawg-webfinger | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text htmlized pdfized bibtex | ||
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| Stream | WG state | WG Document | |
| Document shepherd | Salvatore Loreto | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
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| Send notices to | (None) |
draft-ietf-appsawg-webfinger-07
Network Working Group Paul E. Jones
Internet Draft Gonzalo Salgueiro
Intended status: Standards Track Cisco Systems
Expires: June 2, 2013 Joseph Smarr
Google
December 2, 2012
WebFinger
draft-ietf-appsawg-webfinger-07.txt
Abstract
This specification defines the WebFinger protocol, which can be used
to discover information about people or other entities on the
Internet using standard HTTP methods.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 2, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction...................................................2
2. Terminology....................................................3
3. Overview.......................................................3
4. Example Use of WebFinger.......................................3
4.1. Locating a User's Blog....................................3
4.2. Identity Provider Discovery for OpenID Connect............5
4.3. Auto-Configuration of Email Clients.......................6
4.4. Retrieving Device Information.............................7
5. WebFinger Protocol.............................................8
5.1. Performing a WebFinger Query..............................8
5.2. The JSON Resource Descriptor (JRD)........................9
5.2.1. expires..............................................9
5.2.2. subject.............................................10
5.2.3. aliases.............................................10
5.2.4. properties..........................................10
5.2.5. links...............................................11
5.3. The "rel" Parameter......................................13
5.4. WebFinger and URIs.......................................14
6. Cross-Origin Resource Sharing (CORS)..........................15
7. Access Control................................................15
8. Hosted WebFinger Services.....................................16
9. Security Considerations.......................................17
10. IANA Considerations..........................................18
11. Acknowledgments..............................................19
12. References...................................................19
12.1. Normative References....................................19
12.2. Informative References..................................20
Author's Addresses...............................................20
1. Introduction
WebFinger is used to discover information about people or other
entities on the Internet using standard HTTP [2] methods. The
WebFinger server returns a JavaScript Object Notation (JSON) [5]
object that describes the resource being queried. The JSON object is
referred to as the JSON Resource Descriptor (JRD). The JRD contains
link relations, properties, titles, and other information that is
suitable for automated processing. For a person, the kinds of
information that might be shared via WebFinger include a personal
profile address, identity service, telephone number, or preferred
avatar. For other entities on the Internet, the server might return
JRDs containing link relations that allow a client to discover the
amount of toner in a printer or the physical location of a server.
Information returned via WebFinger might be for direct human
consumption (e.g., looking up someone's phone number), or it might be
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used by systems to help carry out some operation (e.g., facilitate
logging into a web site by determining a user's identity service).
2. Terminology
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 RFC 2119 [1].
WebFinger makes heavy use of "Link Relations". Briefly, a Link
Relation is an attribute and value pair used on the Internet wherein
the attribute identifies the type of link to which the associated
value refers. In Hypertext Transfer Protocol (HTTP) and Web Linking
[4], the attribute is a "rel" and the value is an "href". WebFinger
also uses the "rel" attribute, where the "rel" value is either a
single IANA-registered link relation type [11] or a URI [6].
3. Overview
WebFinger enables the discovery of information about users, devices,
and other entities that are associated with a host. Discovery
involves a single HTTP GET request to the well-known [3] "webfinger"
resource at the target host and receiving back a JavaScript Object
Notation (JSON) [5] Resource Descriptor (JRD) (see section 5.2)
containing link relations, properties, titles, and other useful
information. The request MUST include the URI or IRI [7] for the
entity for which information is sought as a parameter named
"resource".
Use of WebFinger is illustrated in the examples in Section 4, then
described more formally in Section 5.
4. Example Use of WebFinger
This non-normative section shows a few sample uses of WebFinger.
4.1. Locating a User's Blog
Assume you receive an email from Bob and he refers to something he
posted on his blog, but you do not know where Bob's blog is located.
It would be simple to discover the address of Bob's blog if he makes
that information available via WebFinger.
Assume your email client can discover the blog for you. After
receiving the message from Bob (bob@example.com), you instruct your
email client to perform a WebFinger query. It does so by issuing the
following HTTPS query to example.com:
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GET /.well-known/webfinger?
resource=acct%3Abob%40example.com HTTP/1.1
Host: example.com
The server might then respond with a message like this:
HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Content-Type: application/json; charset=UTF-8
{
"expires" : "2012-11-16T19:41:35Z",
"subject" : "acct:bob@example.com",
"aliases" :
[
"http://www.example.com/~bob/"
],
"properties" :
{
"http://example.com/rel/role/" : "employee"
},
"links" :
[
{
"rel" : "http://webfinger.net/rel/avatar",
"type" : "image/jpeg",
"href" : "http://www.example.com/~bob/bob.jpg"
},
{
"rel" : "http://webfinger.net/rel/profile-page",
"href" : "http://www.example.com/~bob/"
},
{
"rel" : "blog",
"type" : "text/html",
"href" : "http://blogs.example.com/bob/",
"titles" :
{
"en-us" : "The Magical World of Bob",
"fr" : "Le monde magique de Bob"
}
},
{
"rel" : "vcard",
"href" : "http://www.example.com/~bob/bob.vcf"
}
]
}
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The email client would take note of the "blog" link relation in the
above JRD that refers to Bob's blog. This URL would then be
presented to you so that you could then visit his blog. The email
client might also note that Bob has published an avatar link relation
and use that picture to represent Bob inside the email client.
Lastly, the client might consider the vcard [15] link relation in
order to update contact information for Bob.
In the above example, an "acct" URI [8] is used in the query, though
any valid alias for the user might also be used. An alias is a URI
that is different from the "subject" URI that identifies the same
entity. In the above example, there is one "http" alias returned,
though there might have been more than one. Had the "http:" URI
shown as an alias been used to query for information about Bob, the
query would have appeared as:
GET /.well-known/webfinger?
resource=http%3A%2F%2Fwww.example.com%2F~bob%2F HTTP/1.1
Host: example.com
The response would have been substantially the same, with the subject
and alias information changed as necessary. Other information, such
as the expiration time might also change, but the set of link
relations and properties would be the same with either response.
4.2. Identity Provider Discovery for OpenID Connect
Suppose Carol wishes to authenticate with a web site she visits using
OpenID Connect [17]. She would provide the web site with her OpenID
Connect identifier, say carol@example.com. The visited web site
would perform a WebFinger query looking for the OpenID Connect
Provider. Since the site is interested in only one particular link
relation, the server might utilize the "rel" parameter as described
in section 5.3:
GET /.well-known/webfinger?
resource=acct%3Acarol%40example.com&
rel=http%3A%2F%2Fopenid.net%2Fspecs%2Fconnect%2F1.0%2Fissuer
HTTP/1.1
Host: example.com
The server might respond with a JRD like this:
{
"expires" : "2012-11-16T19:41:35Z",
"subject" : "acct:carol@example.com",
"aliases" :
[
"http://www.example.com/~carol/"
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],
"properties" :
{
"http://example.com/rel/role/" : "employee"
},
"links" :
[
{
"rel" : "http://openid.net/specs/connect/1.0/issuer",
"href" : "https://openid.example.com/"
}
]
}
Since the "rel" parameter only filters the link relations returned by
the server, other name/value pairs in the response, including any
aliases or properties, would be returned. Also, since support for
the "rel" parameter is optional, the client must not assume the
"links" array will contain only the requested link relation.
4.3. Auto-Configuration of Email Clients
WebFinger could be used to auto-provision an email client with basic
configuration data. Suppose that sue@example.com wants to configure
her email client. Her email client might issue the following query:
GET /.well-known/webfinger?
resource=mailto%3Asue%40example.com HTTP/1.1
Host: example.com
The response from the server would contain entries for the various
protocols, transport options, and security options. If there are
multiple options, the server might return a link relation that for
each of the valid options and the client or Sue might select which
option to choose. Since JRDs list link relations in a specific
order, then the most-preferred choices could be presented first.
Consider this response:
{
"subject" : "mailto:sue@example.com",
"links" :
[
{
"rel" : "http://example.net/rel/smtp-server",
"properties" :
{
"http://example.net/email/host" : "smtp.example.com",
"http://example.net/email/port" : "587",
"http://example.net/email/login-required" : "yes",
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"http://example.net/email/transport" : "starttls"
}
},
{
"rel" : "http://example.net/rel/imap-server",
"properties" :
{
"http://example.net/email/host" : "imap.example.com",
"http://example.net/email/port" : "993",
"http://example.net/email/transport" : "ssl"
}
}
]
}
In this example, you can see that the WebFinger server advertises an
SMTP service and an IMAP service. In this example, the "href"
entries associated with the link relation are absent. This is valid
when there is no external reference that needs to be made.
4.4. Retrieving Device Information
As another example, suppose there are printers on the network and you
would like to check the current toner level for a particular printer
identified via the URI device:p1.example.com. While the "device" URI
scheme is not presently specified, we use it here for illustrative
purposes.
Following the procedures similar to those above, a query may be
issued to get link relations specific to this URI like this:
GET /.well-known/webfinger?resource=
device%3Ap1.example.com HTTP/1.1
Host: example.com
The link relations that are returned for a device may be quite
different than those for user accounts. Perhaps we may see a
response like this:
HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Content-Type: application/json; charset=UTF-8
{
"subject" : "device:p1.example.com",
"links" :
[
{
"rel" : "http://example.com/rel/tipsi",
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"href" : "http://192.168.1.5/npap/"
}
]
}
While this example is fictitious, you can imagine that perhaps the
Transport Independent, Printer/System Interface [16] may be enhanced
with a web interface that allows a device that understands the TIP/SI
web interface specification to query the printer for toner levels.
5. WebFinger Protocol
WebFinger is a simple HTTP-based web service that returns a JSON
Resource Descriptor (JRD) to convey information about an entity on
the Internet and the Cross-Origin Resource Sharing (CORS) [10]
specification to facilitate queries made via a web browser.
This specification defines URI parameters that are passed from the
client to the server when issuing a request. These parameters,
"resource" and "rel", and the parameter values are included in the
"query" component of the URI (see Section 3.4 of RFC 3986). To
construct the "query" component, the client performs the following
steps. First, each parameter value is percent-encoded as per Section
2.1 of RFC 3986. Next, the client constructs a string to be placed
in the query component by concatenating the name of the first
parameter together with an equal sign ("=") and the percent-encoded
parameter value. For any subsequent parameters, the client appends
an ampersand ("&") to the string, the name of the next parameter, an
equal sign, and percent-encoded parameter value. The client MUST NOT
insert any spaces while constructing the string. The order in which
the client places each parameter and its corresponding parameter
value is unspecified.
5.1. Performing a WebFinger Query
WebFinger clients issue queries to the well-known resource /.well-
known/webfinger. All queries MUST include the "resource" parameter
exactly once and set to the value of the URI for which information is
being sought. If the "resource" parameter is absent or malformed,
the WebFinger server MUST return a 400 status code.
Clients MUST query the server using HTTPS and utilize HTTP only if an
HTTPS connection cannot be established, and then only if the client
issuing the query will not utilize information in the response in
such a way as to compromise user security or privacy. As an example,
a client using WebFinger to facilitate logging into a web site MUST
only utilize HTTPS to ensure that a user is not misdirected to a
rogue web site that might steal the user's credentials. If the HTTPS
server has an invalid certificate or returns an HTTP status code
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indicating some error, including a 4xx or 5xx, the client MUST NOT
use HTTP in attempt to complete the discovery.
WebFinger servers MUST return a JRD as the representation for the
resource if the client requests no format explicitly via the HTTP
"Accept" header. A client MAY include the "Accept" header to
indicate a desired representation, though no other representation is
defined in this specification. The media type used for the JSON
Resource Descriptor (JRD) is "application/json" [5].
If the client queries the WebFinger server and provides a URI for
which the server has no information, the server MUST return a 404
status code.
WebFinger servers can include cache validators in a response to
enable conditional requests by clients and/or expiration times as per
RFC 2616 section 13.
5.2. The JSON Resource Descriptor (JRD)
The JSON Resource Descriptor (JRD) is a JSON object that is comprised
of name/value pairs appearing in this RECOMMENDED order:
o expires
o subject
o aliases
o properties
o links
The members "expires" and "subject" are name/value pairs whose value
are strings, "aliases" is an array of strings, "properties" is an
object comprised of name/value pairs whose values are strings, and
"links" is an array of objects that contain link relation
information.
When processing a JRD, the client MUST ignore any unknown member and
not treat the presence of an unknown member as an error.
Below, each of these members of the JRD is described in more detail.
5.2.1. expires
The value of the "expires" member is a string that indicates the date
and time after which the JRD SHOULD be considered expired and no
longer utilized. The format of the date/time string is:
YYYY-MM-DDTHH:MM:SSZ
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Here, "YYYY" indicates the four-digit year, "MM" indicates the two-
digit month (in the range of 01 to 12), and "DD" indicates the two-
digit day of the month (in the range of 01 to 31). The "T" is
literally an ASCII "T" that exists merely as a separator between the
date and the time. The "HH" indicates the two-digit hour of the day
(in the range of 01 to 12), "MM" indicates the two-digit minute of
the day (in the range of 00 to 59), and "SS" indicates the two-digit
number of seconds (in the range of 00 to 59). A colon (":")
character MUST separate the hours, minutes, and seconds values, and a
hyphen ("-") MUST separate the year, month, and day in the string.
The "Z" at the end of the string is literally an ASCII "Z" that
indicates UTC time and MUST be present. The "expires" string MUST
utilize UTC time. An example of the "expires" member is:
"expires" : "2012-11-16T19:41:35Z"
The server MAY include the "expires" header in a JRD and clients
SHOULD honor the value if present.
5.2.2. subject
The value of the "subject" member is a string that MUST be set to the
same value as the "resource" parameter in the client request. This
is a URI that identifies the entity for which the client queried the
server.
The "subject" member MUST be included in the JRD.
5.2.3. aliases
The "aliases" array is an array of zero or more URI strings that
identify the same entity as the "subject" URI. Each URI must be an
absolute URI.
The server MAY include the "aliases" array in the JRD.
5.2.4. properties
The "properties" object is comprised of zero or more name/value pairs
whose names are absolute URIs and whose values are strings or null.
Properties are used to convey additional information about the
subject of the JRD. As an example, consider this use of
"properties":
"properties" : { "http://webfinger.net/rel/name" : "Bob Smith" }
The server MAY include the "properties" member in the JRD.
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5.2.5. links
The "links" array contains zero or more elements that contain the
link relation information. Each element of the array is an object
comprised of the following name/value pairs in this RECOMMENDED
order:
o rel
o type
o href
o titles
o properties
The members "rel", "type", and "href" are a name/value pairs whose
values are strings, "titles" and "properties" are objects comprised
of name/value pairs whose values are strings.
The order of elements in the "links" array indicates an order of
preference. Thus, if there are two or more link relations having the
same "rel" value, the first link relation would indicate the user's
preferred link relation.
Servers MAY include the "links" array in the JRD.
Below, each of the members of the objects found in the "links" array
is described in more detail. Each object in the "links" array,
referred to as a "link relation object", is completely independent
from any other object in the array; any requirement on the server to
include a given member in the link relation object refers only to
that particular object.
5.2.5.1. rel
The value of the "rel" member is a string that is either an absolute
URI or a registered relation type [11] (see RFC 5988 [4]). The value
of the "rel" member MUST contain exactly one URI string or registered
relation type and MUST NOT contain a space-separated list of URIs or
registered relation types. The URI or registered relation type
identifies the type of the link relation. The other members of the
object have meaning only once the type of link relation is
understood. In some instances, the link relation will have
associated semantics that allow a client to query for other resources
on the Internet. In other instances, the link relation will have
associated semantics that allow the client to utilize the other
members of the link relation object without fetching additional
external resources.
Servers MUST include the "rel" member in the link relation object.
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5.2.5.2. type
The value of the "type" member is a string that indicates the media
type [12] of the linked resource (see RFC 4288 [13]).
Servers MAY include the "type" member in the link relation object.
5.2.5.3. href
The value of the "href" member is a string that contains a URI
pointing to the linked resource.
Servers MAY include the "href" member in the link relation object.
5.2.5.4. titles
The "titles" object is comprised of zero or more name/value pairs
whose name is a language tag [14] or the string "default". The
string is human-readable and describes the link relation. More than
one title for the link relation MAY be provided for the benefit of
users who utilize the link relation and, if used, a language
identifier SHOULD be duly used as the name. If the language is
unknown or unspecified, then the name is "default".
A server SHOULD NOT include more than one title named with the same
language tag (or "default") within the link relation object. The
client behavior is undefined if a link relation object includes more
than one title named with the same language tag (or "default"),
though the client MUST NOT treat this as an error. The client can
select whichever title or titles it wishes to utilize.
Here is an example of the titles object:
"titles" :
{
"en-us" : "The Magical World of Bob",
"fr" : "Le monde magique de Bob"
}
The server MAY include the "titles" member in the link relation
object.
5.2.5.5. properties
The "properties" object within the link relation object is comprised
of zero or more name/value pairs whose names are absolute URIs and
whose values are strings or null. Properties are used to convey
additional information about the link relation. As an example,
consider this use of "properties":
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"properties" : { "http://example.net/mail/port" : "993" }
The server MAY include the "properties" member in the link relation
object.
5.3. The "rel" Parameter
When issuing a request to the server, the client MAY utilize the
"rel" parameter to request only a subset of the information that
would otherwise be returned without the "rel" parameter. When the
"rel" parameter is used, only the link relations that match the link
relations provided via "rel" are included in the array of links
returned in the JRD. All other information normally present in a
resource descriptor is present in the resource descriptor, even when
"rel" is employed.
The "rel" parameter MAY be transmitted to the server multiple times
in order to request multiple types of link relations.
The purpose of the "rel" parameter is to return a subset of
resource's link relations. Use of the parameter might reduce
processing requirements on either the client or server, and it might
also reduce the bandwidth required to convey the partial resource
descriptor, especially if there are numerous link relation values to
convey for a given resource.
Support for the "rel" parameter is OPTIONAL, but RECOMMENDED on the
server. Should the server not support the "rel" parameter, it MUST
ignore it and process the request as if no "rel" parameter values
were present.
The following example presents the same example as found in section
4.1, but uses the "rel" parameter in order to select two link
relations:
GET /.well-known/webfinger?
resource=acct%3Abob%40example.com&
rel=http%3A%2F%2Fwebfinger.net%2Frel%2Fprofile-page&
rel=vcard HTTP/1.1
Host: example.com
In this example, the client requests the link relations of type
"http://webfinger.net/rel/profile-page" and "vcard". The server then
responds with a message like this:
HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Content-Type: application/json; charset=UTF-8
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{
"expires" : "2012-11-16T19:41:35Z",
"subject" : "acct:bob@example.com",
"aliases" :
[
"http://www.example.com/~bob/"
],
"properties" :
{
"http://example.com/rel/role/" : "employee"
},
"links" :
[
{
"rel" : "http://webfinger.net/rel/profile-page",
"href" : "http://www.example.com/~bob/"
},
{
"rel" : "vcard",
"href" : "http://www.example.com/~bob/bob.vcf"
}
]
}
As you can see, the server returned only the link relations requested
by the client, but also included the other parts of the JRD.
In the event that a client requests links for link relations that are
not defined for the specified resource, a resource descriptor MUST be
returned. In the returned JRD, the "links" array MAY be absent,
empty, or contain only links that did match a provided "rel" value.
The server MUST NOT return a 404 status code when a particular link
relation specified via "rel" is not defined for the resource, as a
404 status code is reserved for indicating that the resource itself
(e.g., either /.well-known/webfinger or the resource indicated via
the "resource" parameter) does not exist.
5.4. WebFinger and URIs
WebFinger requests can include a parameter specifying the URI of an
account, device, or other entity. WebFinger is agnostic regarding
the scheme of such a URI: it could be an "acct" URI [7], an "http" or
"https" URI, a "mailto" URI, or some other scheme.
For resources associated with a user account at a host, use of the
"acct" URI scheme is RECOMMENDED, since it explicitly identifies an
account accessible via WebFinger. Further, the "acct" URI scheme is
not associated with other protocols as, by way of example, the
"mailto" URI scheme is associated with email. Since not every host
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offers email service, using the "mailto" URI scheme [9] is not ideal
for identifying user accounts on all hosts. That said, use of the
"mailto" URI scheme would be ideal for use with WebFinger to discover
mail server configuration information for a user.
A host MAY utilize one or more URIs that serve as aliases for the
user's account, such as URIs that use the "http" URI scheme [2]. A
WebFinger server MUST return substantially the same response to both
an "acct" URI and any alias URI for the account, including the same
set of link relations and properties. The only name/value pairs in
the response that MAY be different include "subject", "expires", and
"aliases". In addition, the server SHOULD include the entire list
aliases for the user's account in the JRD returned when querying the
LRDD resource or when utilizing the "resource" parameter.
6. Cross-Origin Resource Sharing (CORS)
WebFinger resources might not be accessible from a web browser due to
"Same-Origin" policies. The current best practice is to make
resources available to browsers through Cross-Origin Resource Sharing
(CORS) [10], and servers MUST include the Access-Control-Allow-Origin
HTTP header in responses. Servers SHOULD support the least
restrictive setting by allowing any domain access to the WebFinger
resources:
Access-Control-Allow-Origin: *
There are cases where defaulting to the least restrictive setting is
not appropriate, for example a WebFinger server on an intranet that
provides sensitive company information should not allow CORS requests
from any domain, as that could allow leaking of that sensitive
information. WebFinger servers that wish to restrict access to
information from external entities SHOULD use a more restrictive
Access-Control-Allow-Origin header.
7. Access Control
As with all web resources, access to the /.well-known/webfinger
resource MAY require authentication. Further, failure to provide
required credentials MAY result in the server forbidding access or
providing a different response than had the client authenticated with
the server.
Likewise, a server MAY provide different responses to different
clients based on other factors, such as whether the client is inside
or outside a corporate network. As a concrete example, a query
performed on the internal corporate network might return link
relations to employee pictures, whereas link relations for employee
pictures might not be provided to external entities.
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Further, link relations provided in a WebFinger server response MAY
point to web resources that impose access restrictions. For example,
the aforementioned corporate server may provide both internal and
external entities with URIs to employee pictures, but further
authentication might be required in order for the client to access
the picture resources if the request comes from outside the corporate
network.
The decisions made with respect to what set of link relations a
WebFinger server provides to one client versus another and what
resources require further authentication, as well as the specific
authentication mechanisms employed, are outside the scope of this
document.
8. Hosted WebFinger Services
As with most services provided on the Internet, it is possible for a
domain owner to utilize "hosted" WebFinger services. By way of
example, a domain owner might control most aspects of their domain,
but use a third-party hosting service for email. In the case of
email, mail servers for a domain are identified by MX records. An MX
record points to the mail server to which mail for the domain should
be delivered. It does not matter to the sending mail server whether
those MX records point to a server in the destination domain or a
different domain.
Likewise, a domain owner might utilize the services of a third party
to provide WebFinger services on behalf of its users. Just as a
domain owner was required to insert MX records into DNS to allow for
hosted email serves, the domain owner is required to redirect HTTP(S)
queries to its domain to allow for hosted WebFinger services.
When a query is issued to /.well-known/webfinger, the web server MUST
return a 301, 302, or 307 response status code that includes a
Location header pointing to the location of the hosted WebFinger
service URL. The WebFinger service URL does not need to point to
/.well-known/* on the hosting service provider server. WebFinger
clients MUST follow all 301, 302, or 307 redirection requests.
As an example, assume that example.com's WebFinger services are
hosted by example.net. Suppose a client issues a query for
acct:alice@example.com like this:
GET /.well-known/webfinger?
resource=acct%3Aalice%40example.com HTTP/1.1
Host: example.com
The server might respond with this:
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HTTP/1.1 307 Temporary Redirect
Location: http://wf.example.net/example.com/webfinger?
resource=acct%3Aalice%40example.com HTTP/1.1
The client MUST follow the redirection, re-issuing the request to the
URL provided in the Location header.
9. Security Considerations
Since this specification utilizes Cross-Origin Resource Sharing
(CORS) [10], all of the security considerations applicable CORS are
also applicable to this specification.
The recommended use of HTTPS is to ensure that information is not
modified during transit. It should be appreciated that in
environments where an HTTPS server is normally available, there
exists the possibility that a compromised network might have its
WebFinger server operating on HTTPS replaced with one operating only
over HTTP. As such, clients that need to ensure data is not
compromised SHOULD NOT issue queries over a non-secure connection.
While Section 5.1 allows for clients that fail to establish an HTTPS
connection to attempt a query using HTTP, a client and any underlying
client libraries are not required to re-issue queries using HTTP and
SHOULD NOT when security for a given application that uses WebFinger
is paramount.
When using HTTPS, clients MUST verify that the certificate used on an
HTTPS connection is valid.
Service providers and users should be aware that placing information
on the Internet accessible through WebFinger means that any user can
access that information. While WebFinger can be an extremely useful
tool for allowing quick and easy access to one's avatar, blog, or
other personal information, users should understand the risks, too.
If one does not wish to share certain information with the world, do
not allow that information to be freely accessible through WebFinger
and do not use any service supporting WebFinger. Further, WebFinger
servers MUST NOT be used to provide any personal information to any
party unless explicitly or implicitly authorized by the person whose
information is being shared. Implicit authorization can be determined
by the user's voluntary utilization of a service as defined by that
service's relevant terms of use or published privacy policy.
The aforementioned word of caution is perhaps worth emphasizing again
with respect to dynamic information one might wish to share, such as
the current location of a user. WebFinger can be a powerful tool
used to assemble information about a person all in one place, but
service providers and users should be mindful of the nature of that
information shared and the fact that it might be available for the
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entire world to see. Sharing location information, for example,
would potentially put a person in danger from any individual who
might seek to inflict harm on that person.
The easy access to user information via WebFinger was a design goal
of the protocol, not a limitation. If one wishes to limit access to
information available via WebFinger, such as a WebFinger server for
use inside a corporate network, the network administrator must take
measures necessary to limit access from outside the network. Using
standard methods for securing web resources, network administrators
do have the ability to control access to resources that might return
sensitive information. Further, WebFinger servers can be employed in
such a way as to require authentication and prevent disclosure of
information to unauthorized entities.
Finally, a WebFinger server has no means of ensuring that information
provided by a user is accurate. Likewise, neither the server nor the
client can be absolutely guaranteed that information has not been
manipulated either at the server or along the communication path
between the client and server. Use of HTTPS helps to address some
concerns with manipulation of information along the communication
path, but it clearly cannot address issues where the server provided
incorrect information, either due to being provided false information
or due to malicious behavior on the part of the server administrator.
As with any information service available on the Internet, users
should wary of information received from untrusted sources.
10. IANA Considerations
This specification registers the "webfinger" well-known URI in the
Well-Known URI Registry as defined by [3].
URI suffix: webfinger
Change controller: IETF
Specification document(s): RFC QQQ
Related information: The response from WebFinger server will be a
JSON Resource Descriptor (JRD) as described in Section 5.2 of RFC
QQQ.
[RFC EDITOR: Please replace "QQQ" references in this section with the
number for this RFC.]
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11. Acknowledgments
The authors would like to acknowledge Eran Hammer-Lahav, Blaine Cook,
Brad Fitzpatrick, Laurent-Walter Goix, Joe Clarke, Michael B. Jones,
Peter Saint-Andre, Dick Hardt, Tim Bray, and Joe Gregorio for their
invaluable input.
12. References
12.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] 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.
[3] Nottingham, M., Hammer-Lahav, E., "Defining Well-Known Uniform
Resource Identifiers (URIs)", RFC 5785, April 2010.
[4] Nottingham, M., "Web Linking", RFC 5988, October 2010.
[5] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
[6] Berners-Lee, T., Fielding, R., and Masinter, L., "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
January 2005.
[7] Duerst, M., "Internationalized Resource Identifiers (IRIs)",
RFC 3987, January 2005.
[8] Saint-Andre, P., "The 'acct' URI Scheme", draft-ietf-appsawg-
acct-uri-01, October 2012.
[9] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto' URI
Scheme", RFC 6068, October 2010.
[10] Van Kesteren, A., "Cross-Origin Resource Sharing", W3C CORS
http://www.w3.org/TR/cors/, July 2010.
[11] IANA, "Link Relations", http://www.iana.org/assignments/link-
relations/.
[12] IANA, "MIME Media Types",
http://www.iana.org/assignments/media-types/index.html.
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[13] Freed, N., Klensin, J., "Media Type Specifications and
Registration Procedures", RFC 4288, December 2005.
[14] Phillips, A., Davis, M., "Tags for Identifying Languages", RFC
5646, January 2001.
12.2. Informative References
[15] Perreault, S., "vCard Format Specification", RFC 6350, August
2011.
[16] "Transport Independent, Printer/System Interface", IEEE Std
1284.1-1997, 1997.
[17] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B.,
Mortimore, C., and E. Jay, "OpenID Connect Messages 1.0", June
2012, http://openid.net/specs/openid-connect-messages-1_0.html.
Author's Addresses
Paul E. Jones
Cisco Systems, Inc.
7025 Kit Creek Rd.
Research Triangle Park, NC 27709
USA
Phone: +1 919 476 2048
Email: paulej@packetizer.com
IM: xmpp:paulej@packetizer.com
Gonzalo Salgueiro
Cisco Systems, Inc.
7025 Kit Creek Rd.
Research Triangle Park, NC 27709
USA
Phone: +1 919 392 3266
Email: gsalguei@cisco.com
IM: xmpp:gsalguei@cisco.com
Joseph Smarr
Google
Email: jsmarr@google.com
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