Network Working Group Paul E. Jones
Internet Draft Gonzalo Salgueiro
Intended status: Standards Track Cisco Systems
Expires: August 8, 2013 Joseph Smarr
Google
February 8, 2013
WebFinger
draft-ietf-appsawg-webfinger-10.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. WebFinger discovers
information for a URI that might not be usable as a locator
otherwise, such as account or email URIs.
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
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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 August 8, 2013.
Copyright Notice
Copyright (c) 2013 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
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction...................................................2
2. Terminology....................................................3
3. Example Uses of WebFinger......................................3
3.1. Locating a User's Blog....................................3
3.2. Identity Provider Discovery for OpenID Connect............5
3.3. Auto-Configuration of Email Clients.......................6
3.4. Retrieving Device Information.............................7
4. WebFinger Protocol.............................................8
4.1. Constructing a WebFinger Request URI......................8
4.2. Performing a WebFinger Query..............................9
4.3. The "rel" Parameter.......................................9
4.4. The JSON Resource Descriptor (JRD).......................11
4.4.1. subject.............................................11
4.4.2. aliases.............................................12
4.4.3. properties..........................................12
4.4.4. links...............................................12
4.5. WebFinger and URIs.......................................14
5. Cross-Origin Resource Sharing (CORS)..........................14
6. Access Control................................................15
7. Hosted WebFinger Services.....................................15
8. Security Considerations.......................................16
9. IANA Considerations...........................................18
9.1. Well-Known URI...........................................18
9.2. JSON Resource Descriptor (JRD) Media Type................18
10. Acknowledgments..............................................20
11. References...................................................20
11.1. Normative References....................................20
11.2. Informative References..................................21
Author's Addresses...............................................22
1. Introduction
WebFinger is used to discover information about people or other
entities on the Internet that are identified by a URI [6] or IRI [7]
using standard Hypertext Transfer Protocol (HTTP) [2] methods over a
secure transport [14]. A WebFinger resource returns a JavaScript
Object Notation (JSON) [5] object describing the entity that is
queried. The JSON object is referred to as the JSON Resource
Descriptor (JRD).
For a person, the kinds of information that might be discoverable via
WebFinger include a personal profile address, identity service,
telephone number, or preferred avatar. For other entities on the
Internet, a WebFinger resource might return JRDs containing link
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relations [10] that enable a client to discover, for example, 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
used by systems to help carry out some operation (e.g., facilitate
logging into a web site by determining a user's identity service).
Use of WebFinger is illustrated in the examples in Section 3 and
described more formally in Section 4.
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". A Link Relation is an
attribute-and-value pair in which the attribute identifies the type
of relationship between the linked entity or resource and the
information specified in the value. In Web Linking [4], the link
relation is represented using an HTTP entity-header of "Link", where
the "rel" attribute specifies the type of relationship and the "href"
attribute specifies the information that is linked to the entity or
resource. In WebFinger, the same concept is represented using a JSON
array of "links" objects, where each member named "rel" specifies the
type of relationship and each member named "href" specifies the
information that is linked to the entity or resource. Note that
WebFinger narrows the scope of a link relation beyond what is defined
for Web Linking by stipulating that the value of the "rel" member
needs to be either a single IANA-registered link relation type [10]
or a URI [6].
3. Example Uses of WebFinger
This non-normative section shows a few sample uses of WebFinger.
3.1. 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 made
that information available via WebFinger.
Assume your email client can discover the blog for you. After
receiving the message from Bob (bob@example.com), your email client
performs a WebFinger query either automatically or at your command.
It does so by issuing the following HTTPS [14] 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/jrd+json
{
"subject" : "acct:bob@example.com",
"aliases" :
[
"http://www.example.com/~bob/"
],
"properties" :
{
"http://example.com/ns/role/" : "employee"
},
"links" :
[
{
"rel" : "http://webfinger.example/rel/avatar",
"type" : "image/jpeg",
"href" : "http://www.example.com/~bob/bob.jpg"
},
{
"rel" : "http://webfinger.example/rel/profile-page",
"href" : "http://www.example.com/~bob/"
},
{
"rel" : "http://webfinger.example/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" : "http://webfinger.example/rel/businesscard",
"href" : "https://www.example.com/~bob/bob.vcf"
}
]
}
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The email client would take note of the link relation in the above
JRD that refers to Bob's blog. The blog's URI 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 automatically retrieve the data located at
the URI specified by the "businesscard" link relation (which might be
a vcard [16]) to update the information about Bob in its internal
address book.
In the above example, an "acct" URI [8] is used in the query, though
any valid alias for the user might also be used. See Section 4.5 for
more information on WebFinger and URIs.
An alias is a URI that is different from the "subject" URI, yet
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: www.example.com
Note that the host queried in this example is different than for the
acct URI example, since the URI refers to a different host. Either
this host would provide a response, or it would redirect the client
to another host (e.g., redirect back to example.com). Either way,
the response would have been substantially the same, with the subject
and alias information changed as necessary.
3.2. Identity Provider Discovery for OpenID Connect
Suppose Carol wishes to authenticate with a web site she visits using
OpenID Connect [18]. 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 WebFinger resource might utilize the "rel" parameter as
described in Section 4.3:
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 like this:
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HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Content-Type: application/jrd+json
{
"subject" : "acct:carol@example.com",
"links" :
[
{
"rel" : "http://openid.net/specs/connect/1.0/issuer",
"href" : "https://openid.example.com"
}
]
}
Since the "rel" parameter only serves to filter the link relations
returned by the resource, 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.
3.3. 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 returned resource representation would contain entries for the
various protocols, transport options, and security options. If there
are multiple options, the resource representation might include a
link relation 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:
HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Content-Type: application/jrd+json
{
"subject" : "mailto:sue@example.com",
"links" :
[
{
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"rel" : "http://webfinger.example/rel/smtp-server",
"properties" :
{
"http://webfinger.example/email/host" : "smtp.example.com",
"http://webfinger.example/email/port" : "587",
"http://webfinger.example/email/login-required" : "yes",
"http://webfinger.example/email/transport" : "starttls"
}
},
{
"rel" : "http://webfinger.example/rel/imap-server",
"properties" :
{
"http://webfinger.example/email/host" : "imap.example.com",
"http://webfinger.example/email/port" : "993",
"http://webfinger.example/email/transport" : "ssl"
}
}
]
}
In this example, you can see that the WebFinger resource
representation 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 additional reference that
needs to be made.
3.4. 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: p1.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/jrd+json
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{
"subject" : "device:p1.example.com",
"links" :
[
{
"rel" : "http://webfinger.example/rel/tipsi",
"href" : "http://192.168.1.5/npap/"
}
]
}
While this example is fictitious, you can imagine that perhaps the
Transport Independent, Printer/System Interface [17] may be enhanced
with a web interface enabling a device that understands the TIP/SI
web interface specification to query the printer for toner levels.
4. WebFinger Protocol
A WebFinger resource is a well-known URI [3] using the HTTPS scheme.
WebFinger resources MUST NOT be served with any other URI scheme
(such as HTTP).
GET requests to a WebFinger resource convey the URI to perform the
query upon in the URI's query string; see Section 4.1 for details.
The WebFinger resource returns a JSON Resource Descriptor (JRD) as
the resource representation to convey information about an entity on
the Internet. Also, the Cross-Origin Resource Sharing (CORS) [9]
specification is utilized to facilitate queries made via a web
browser.
4.1. Constructing a WebFinger Request URI
This specification defines parameters that can be passed from the
client to the WebFinger resource 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, so that it conforms to the query
production in Section 3.4 of that specification, and additionally any
instances of the "=" and "&" characters are also percent-encoded.
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 the
parameter value. The client MUST NOT insert any spaces while
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constructing the string. The order in which the client places each
attribute-and-value pair within the query component is unspecified.
4.2. Performing a WebFinger Query
A WebFinger client issues a query to the well-known [3] resource
identified by the URI whose path component begins with "/.well-
known/webfinger" and whose query component 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 resource MUST indicate that the
request is bad as per Section 10.4.1 of RFC 2616 [2].
A client MUST query the WebFinger resource using HTTPS only. If the
client determines that the resource has an invalid certificate, the
resource returns a 4xx or 5xx status code, or the HTTPS connection
cannot be established for any reason, then the client MUST accept
that the WebFinger query has failed and MUST NOT attempt to reissue
the WebFinger request using HTTP over a non-secure connection.
A WebFinger resource MUST return a JRD as the representation for the
resource if the client requests no other supported format explicitly
via the HTTP "Accept" header. The client MAY include the "Accept"
header to indicate a desired representation, though no other
representation than JRD is defined in this specification. The media
type used for the JSON Resource Descriptor (JRD) is
"application/jrd+json" (see Section 9.2).
A WebFinger resource MAY redirect the client, but MUST only redirect
the client to an HTTPS URI.
A WebFinger resource can include cache validators in a response to
enable conditional requests by the client and/or expiration times as
per Section 13 of RFC 2616.
4.3. The "rel" Parameter
When issuing a request to a WebFinger resource, 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 the "rel" parameter are
included in the array of links returned in the JRD. All other
information present in a resource descriptor remains present, even
when "rel" is employed.
The "rel" parameter MAY be transmitted to the WebFinger resource
multiple times in order to request multiple types of link relations.
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The purpose of the "rel" parameter is to return a subset of "link
relation objects" (see Section 4.4.4) that would otherwise be
returned in the resource descriptor. 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" value.
WebFinger resources SHOULD support the "rel" parameter. If the
resource does not support the "rel" parameter, it MUST ignore the
parameter and process the request as if no "rel" parameter values
were present.
The following example presents the same example as found in Section
3.1, but uses the "rel" parameter to select two link relations:
GET /.well-known/webfinger?
resource=acct%3Abob%40example.com&
rel=http%3A%2F%2Fwebfinger.example%2Frel%2Fprofile-page&
rel=http://webfinger.example/rel/businesscard HTTP/1.1
Host: example.com
In this example, the client requests the link relations of type
"http://webfinger.example/rel/profile-page" and
"http://webfinger.example/rel/businesscard". The server then
responds with a message like this:
HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Content-Type: application/jrd+json
{
"subject" : "acct:bob@example.com",
"aliases" :
[
"http://www.example.com/~bob/"
],
"properties" :
{
"http://example.com/ns/role/" : "employee"
},
"links" :
[
{
"rel" : "http://webfinger.example/rel/profile-page",
"href" : "http://www.example.com/~bob/"
},
{
"rel" : "http://webfinger.example/rel/businesscard",
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"href" : "http://www.example.com/~bob/bob.vcf"
}
]
}
As you can see in the response, the resource representation contains
only the link relations requested by the client, but the other parts
of the JRD are still present.
In the event that a client requests link relation types 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.
4.4. The JSON Resource Descriptor (JRD)
The JSON Resource Descriptor (JRD), originally introduced in RFC 6415
[19] and based on the Extensible Resource Descriptor (XRD) format
[20], is a JSON object that is comprised of the following name/value
pairs:
o subject
o aliases
o properties
o links
The member "subject" is a name/value pair whose value is a string,
"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.
4.4.1. subject
The value of the "subject" member is a URI that identifies the entity
that the JRD describes.
The "subject" value returned by a WebFinger resource MAY differ from
the value of the "resource" parameter used in the client's request.
This might happen, for example, when the subject's identity changes
(e.g., a user moves his or her account to another service) or when
the resource prefers to express URIs in canonical form.
The "subject" member MUST be present in the JRD.
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4.4.2. 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 "aliases" array is OPTIONAL in the JRD.
4.4.3. 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.example/ns/name" : "Bob Smith" }
The "properties" member is OPTIONAL in the JRD.
4.4.4. links
The "links" array has any number of member objects, each of which
represents a link [4]. Each of these link objects can have the
following members:
o rel
o type
o href
o titles
o properties
The "rel" and "href" members are strings representing the link's
relation type and the target IRI, respectively. The context of the
link is the "subject" (see Section 4.4.1).
The "type" member is a string indicating what the media type of the
result of dereferencing the link ought to be.
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.
The "links" array is OPTIONAL 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
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from any other object in the array; any requirement to include a
given member in the link relation object refers only to that
particular object.
4.4.4.1. rel
The value of the "rel" member is a string that is either an absolute
URI or a registered relation type [10] (see RFC 5988 [4]). The value
of the "rel" member MUST contain exactly one URI or registered
relation type. 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 enabling
the client to query for other resources on the Internet. In other
instances, the link relation will have associated semantics enabling
the client to utilize the other members of the link relation object
without fetching additional external resources.
The "rel" member MUST be present in the link relation object.
4.4.4.2. type
The value of the "type" member is a string that indicates the media
type [11] of the target resource (see RFC 6838 [12]).
The "type" member is OPTIONAL in the link relation object.
4.4.4.3. href
The value of the "href" member is a string that contains a URI
pointing to the target resource.
The "href" member is OPTIONAL in the link relation object.
4.4.4.4. titles
The "titles" object is comprised of zero or more name/value pairs
whose name is a language tag [13] 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 JRD SHOULD NOT include more than one title identified with the same
language tag (or "default") within the link relation object. Meaning
is undefined if a link relation object includes more than one title
named with the same language tag (or "default"), though this MUST NOT
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be treated as an error. A client MAY 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 "titles" member is OPTIONAL in the link relation object.
4.4.4.5. 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":
"properties" : { "http://webfinger.example/mail/port" : "993" }
The "properties" member is OPTIONAL in the link relation object.
4.5. WebFinger and URIs
WebFinger requests can include a "resource" parameter (see Section
4.1) specifying the URI of an account, device, or other entity.
WebFinger is neutral regarding the scheme of such a URI: it could be
an "acct" URI [7], an "http" or "https" URI, a "mailto" URI [21], or
some other scheme.
To perform a WebFinger lookup on an account specific to the host
being queried, 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 offers email service, using the "mailto" URI
scheme 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.
5. 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
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(CORS) [9], 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
resource:
Access-Control-Allow-Origin: *
There are cases where defaulting to the least restrictive setting is
not appropriate, for example a 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. A
server that wishes to restrict access to information from external
entities SHOULD use a more restrictive Access-Control-Allow-Origin
header.
6. Access Control
As with all web resources, access to the 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 WebFinger resource 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.
Further, link relations provided in a WebFinger resource
representation 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 resource 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.
7. 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
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email, MX records identify mail servers for a domain. 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
queries to its domain to allow for hosted WebFinger services.
When a query is issued to the WebFinger resource, the web server MUST
return a response with a redirection status code that includes a
Location header pointing to the location of the hosted WebFinger
service URI. This WebFinger service URI does not need to point to
the well-known WebFinger location on the hosting service provider
server.
As an example, assume that example.com's WebFinger services are
hosted by wf.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:
HTTP/1.1 307 Temporary Redirect
Access-Control-Allow-Origin: *
Location: https://wf.example.net/example.com/webfinger?
resource=acct%3Aalice%40example.com HTTP/1.1
The client can then follow the redirection, re-issuing the request to
the URI provided in the Location header. Note that the server will
include any required URI parameters in the Location header value,
which could be different than the URI parameters the client
originally used.
8. Security Considerations
Since this specification utilizes Cross-Origin Resource Sharing
(CORS) [9], all of the security considerations applicable to CORS are
also applicable to this specification.
The use of HTTPS is REQUIRED to ensure that information is not
modified during transit. It should be appreciated that in
environments where a web server is normally available, there exists
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the possibility that a compromised network might have its WebFinger
resource operating on HTTPS replaced with one operating only over
HTTP. As such, clients MUST NOT issue queries over a non-secure
connection.
Clients MUST verify that the certificate used on an HTTPS connection
is valid (as defined in [14]) and accept a response only if the
certificate is valid.
Service providers and users should be aware that placing information
on the Internet means that any user can access that information and
WebFinger can be used to make it even easier to discover that
information. While WebFinger can be an extremely useful tool for
discovering 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 on the Internet or discoverable via WebFinger.
Further, WebFinger 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.
The aforementioned word of caution is perhaps worth emphasizing again
with respect to information that might reveal a user's current
context (e.g., the user's location). The power of WebFinger comes
from providing a single place where others can find pointers to
information about a person, 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 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 WebFinger resources for
use inside a corporate network, the network administrator needs to
take necessary measures 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, a server can be
employed in such a way as to require authentication and prevent
disclosure of information to unauthorized entities.
Finally, a WebFinger resource has no means of ensuring that
information provided by a user is accurate. Likewise, neither the
resource 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
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resource 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 be wary of information received from
untrusted sources.
9. IANA Considerations
9.1. Well-Known URI
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 XXXX
Related information: The response representation returned by a
WebFinger resource will be a JSON Resource Descriptor (JRD) as
described in Section 4.4 of RFC XXXX.
[RFC EDITOR: Please replace "XXXX" references in this section and the
following section with the number for this RFC.]
9.2. JSON Resource Descriptor (JRD) Media Type
This specification registers the media type application/jrd+json for
use with WebFinger in accordance with media type registration
procedures defined in [12].
Type name: application
Subtype name: jrd+json
Required parameters: N/A
Optional parameters: N/A
In particular, because RFC 4627 already defines the character
encoding for JSON, no "charset" parameter is used.
Encoding considerations: See RFC 6839, section 3.1.
Security considerations:
The JSON Resource Descriptor (JRD) is a JavaScript Object Notation
(JSON) object. It is a text format that must be parsed by entities
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that wish to utilize the format. Depending on the language and
mechanism used to parse a JSON object, it is possible for an
attacker to inject behavior into a running program. Therefore,
care must be taken to properly parse a received JRD to ensure that
only a valid JSON object is present and that no JavaScript or other
code is injected or executed unexpectedly.
Interoperability considerations:
This media type is a JavaScript Object Notation (JSON) object and
can be consumed by any software application that can consume JSON
objects.
Published specification: RFC XXXX
Applications that use this media type:
The JSON Resource Descriptor (JRD) is used by the WebFinger
protocol (RFC XXXX) to enable the exchange of information between a
client and a WebFinger resource over HTTPS.
Fragment identifier considerations:
The syntax and semantics of fragment identifiers SHOULD be as
specified for "application/json". (At publication of this
document, there is no fragment identification syntax defined for
"application/json".)
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): jrd
Macintosh file type code(s): N/A
Person & email address to contact for further information:
Paul E. Jones <paulej@packetizer.com>
Intended usage: COMMON
Restrictions on usage: N/A
Author: Paul E. Jones <paulej@packetizer.com>
Change controller:
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IESG has change control over this registration.
Provisional registration? (standards tree only): N/A
10. Acknowledgments
This document has benefited from extensive discussion and review of
many of the members of the APPSAWG working group. The authors would
like to especially acknowledge the invaluable input of Eran Hammer-
Lahav, Blaine Cook, Brad Fitzpatrick, Laurent-Walter Goix, Joe
Clarke, Michael B. Jones, Peter Saint-Andre, Dick Hardt, Tim Bray,
James Snell, Melvin Carvalho, Evan Prodromou, Mark Nottingham, Barry
Leiba, Elf Pavlik, Bjoern Hoehrmann, SM, Joe Gregorio and others that
we have undoubtedly, but inadvertently, missed. Special thanks go to
the chairs of APPSAWG, especially Salvatore Loreto for his assistance
in shepherding this document.
11. References
11.1. 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-02, December 2012.
[9] Van Kesteren, A., "Cross-Origin Resource Sharing", W3C CORS
http://www.w3.org/TR/cors/, July 2010.
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[10] IANA, "Link Relations", http://www.iana.org/assignments/link-
relations/.
[11] IANA, "MIME Media Types",
http://www.iana.org/assignments/media-types/index.html.
[12] Freed, N., Klensin, J., Hansen, T., "Media Type Specifications
and Registration Procedures", RFC 6838, January 2013.
[13] Phillips, A., Davis, M., "Tags for Identifying Languages", RFC
5646, January 2001.
[14] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[15] Klyne, G., Newman, C., "Date and Time on the Internet:
Timestamps", RFC 3339, July 2002.
11.2. Informative References
[16] Perreault, S., "vCard Format Specification", RFC 6350, August
2011.
[17] "Transport Independent, Printer/System Interface", IEEE Std
1284.1-1997, 1997.
[18] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B.,
Mortimore, C., and E. Jay, "OpenID Connect Messages 1.0",
January 2013, http://openid.net/specs/openid-connect-messages-
1_0.html.
[19] Hammer-Lahav, E. and Cook, B., "Web Host Metadata", RFC 6415,
October 2011.
[20] Hammer-Lahav, E. and W. Norris, "Extensible Resource Descriptor
(XRD) Version 1.0", http://docs.oasis-
open.org/xri/xrd/v1.0/xrd-1.0.html.
[21] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto' URI
Scheme", RFC 6068, October 2010.
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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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