draft-jones-appsawg-webfinger-02.txt   draft-jones-appsawg-webfinger-03.txt 
Network Working Group Paul E. Jones Network Working Group Paul E. Jones
Internet Draft Gonzalo Salgueiro Internet Draft Gonzalo Salgueiro
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: September 28, 2012 Joseph Smarr Expires: October 9, 2012 Joseph Smarr
Google Google
March 28, 2012 April 9, 2012
Webfinger WebFinger
draft-jones-appsawg-webfinger-02.txt draft-jones-appsawg-webfinger-03.txt
Abstract Abstract
This specification defines the Webfinger protocol. Webfinger may be This specification defines the WebFinger protocol. WebFinger may be
used to discover information about people on the Internet, such as a used to discover information about people on the Internet, such as a
person's personal profile address, identity service, telephone person's personal profile address, identity service, telephone
number, or preferred avatar. Webfinger may also be used to learn number, or preferred avatar. WebFinger may also be used to learn
information about objects on the network, such as the amount of toner information about objects on the network, such as the amount of toner
in a printer or the physical location of a server. in a printer or the physical location of a server.
Status of this Memo Status of this Memo
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This Internet-Draft will expire on September 28, 2012. This Internet-Draft will expire on October 9, 2012.
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Table of Contents Table of Contents
1. Introduction...................................................2 1. Introduction...................................................2
2. Terminology....................................................3 2. Terminology....................................................3
3. Example Uses of Webfinger......................................3 3. Example Uses of WebFinger......................................3
3.1. Locating a User's Blog....................................3 3.1. Locating a User's Blog....................................3
3.2. Retrieving a Person's Contact Information.................5 3.2. Retrieving a Person's Contact Information.................5
3.3. Simplifying the Login Process.............................6 3.3. Simplifying the Login Process.............................6
3.4. Retrieving Device Information.............................7 3.4. Retrieving Device Information.............................7
4. Webfinger Protocol.............................................8 4. WebFinger Protocol.............................................8
4.1. Performing a Webfinger Query..............................8 4.1. Performing a WebFinger Query..............................8
4.2. The Web Host Metadata "resource" Parameter................9 4.2. The Web Host Metadata "resource" Parameter................9
5. The "acct" URI................................................11 4.3. The Web Host Metadata "rel" Parameter....................11
5.1. Using the "acct" URI.....................................11 5. The "acct" URI................................................12
5.2. Syntax of "acct" URI.....................................11 5.1. Using the "acct" URI.....................................12
6. The "acct" Link Relation......................................12 5.2. Syntax of "acct" URI.....................................13
6.1. Purpose for the "acct" Link Relation.....................12 6. The "acct" Link Relation......................................13
6.2. Example Message Exchange Using the "acct" Link Relation..13 6.1. Purpose for the "acct" Link Relation.....................13
7. Cross-Origin Resource Sharing (CORS)..........................13 6.2. Example Message Exchange Using the "acct" Link Relation..14
8. Security Considerations.......................................14 7. Cross-Origin Resource Sharing (CORS)..........................15
9. IANA Considerations...........................................14 8. Security Considerations.......................................15
9.1. Registration of the "acct" URI scheme name...............15 9. IANA Considerations...........................................16
9.2. Registration of the "acct" Link Relation Type............15 9.1. Registration of the "acct" URI scheme name...............16
10. Acknowledgments..............................................16 9.2. Registration of the "acct" Link Relation Type............16
11. References...................................................16 10. Acknowledgments..............................................17
11.1. Normative References....................................16 11. References...................................................17
11.2. Informative References..................................17 11.1. Normative References....................................17
Author's Addresses...............................................18 11.2. Informative References..................................18
Author's Addresses...............................................19
1. Introduction 1. Introduction
There is a utility found on UNIX systems called "finger" [14] that There is a utility found on UNIX systems called "finger" [14] that
allows a person to access information about another person. The allows a person to access information about another person. The
information being queried might be on a computer anywhere in the information being queried might be on a computer anywhere in the
world. The information returned via "finger" is simply a plain text world. The information returned via "finger" is simply a plain text
file that contains unstructured information provided by the queried file that contains unstructured information provided by the queried
user. user.
Webfinger borrows the concept of the legacy finger protocol, but WebFinger borrows the concept of the legacy finger protocol, but
introduces a very different approach to sharing information. Rather introduces a very different approach to sharing information. Rather
than returning a simple unstructured text file, Webfinger uses than returning a simple unstructured text file, Webfinger uses
structured documents that contain link relations. These link structured documents that contain link relations. These link
relations point to information a user or entity on the Internet relations point to information a user or entity on the Internet
wishes to expose. For a person, the kinds of information that might wishes to expose. For a person, the kinds of information that might
be exposed include a personal profile address, identity service, be exposed include a personal profile address, identity service,
telephone number, or preferred avatar. Webfinger may also be used to telephone number, or preferred avatar. WebFinger may also be used to
learn information about objects on the network, such as the amount of learn information about objects on the network, such as the amount of
toner in a printer or the physical location of a server. toner in a printer or the physical location of a server.
Information returned via Webfinger might be for direct human Information returned via WebFinger might be for direct human
consumption (e.g., another user's phone number) or it might be used consumption (e.g., another user's phone number) or it might be used
by systems to help carry out some operation (e.g., facilitate logging by systems to help carry out some operation (e.g., facilitate logging
into a web site by determining a user's identification service). into a web site by determining a user's identification service).
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1]. document are to be interpreted as described in RFC 2119 [1].
"SHOULD", "SHOULD NOT", "RECOMMENDED", and "NOT RECOMMENDED" are WebFinger makes heavy use of "Link Relations". Briefly, a Link
appropriate when valid exceptions to a general requirement are known
to exist or appear to exist, and it is infeasible or impractical to
enumerate all of them. However, they should not be interpreted as
permitting implementors to fail to implement the general requirement
when such failure would result in interoperability failure.
Webfinger makes heavy use of "Link Relations". Briefly, a Link
Relation is an attribute and value pair used on the Internet wherein Relation is an attribute and value pair used on the Internet wherein
the attribute identifies the type of link to which the associated the attribute identifies the type of link to which the associated
value refers. In Hypertext Transfer Protocol (HTTP) [2] and Web value refers. In Hypertext Transfer Protocol (HTTP) [2] and Web
Linking [3], the attribute is a "rel" and the value is an "href". Linking [3], the attribute is a "rel" and the value is an "href".
3. Example Uses of Webfinger 3. Example Uses of WebFinger
In this section, we describe just a few sample uses for Webfinger and In this section, we describe just a few sample uses for WebFinger and
show what the protocol looks like. This is not an exhaustive list of show what the protocol looks like. This is not an exhaustive list of
possible uses and the entire section should be considered non- possible uses and the entire section should be considered non-
normative. The list of potential use cases is virtually unlimited normative. The list of potential use cases is virtually unlimited
since a user can share any kind of machine-consumable information via since a user can share any kind of machine-consumable information via
Webfinger. WebFinger.
3.1. Locating a User's Blog 3.1. Locating a User's Blog
Assume you receive an email from Bob and he refers to something he 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. 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 It would be simple to discover the address of Bob's blog if he makes
that information available via Webfinger. that information available via WebFinger.
Let's assume your email client discovers that blog automatically for Let's assume your email client discovers that blog automatically for
you. After receiving the message from Bob (bob@example.com), your you. After receiving the message from Bob (bob@example.com), your
email client performs the following steps behind the scenes. email client performs the following steps behind the scenes.
First, it tries to get the host metadata [9] information for the First, it tries to get the host metadata [9] information for the
domain example.com. It does this by issuing the following HTTPS domain example.com. It does this by issuing the following HTTPS
query to example.com: query to example.com:
GET /.well-known/host-meta HTTP/1.1 GET /.well-known/host-meta HTTP/1.1
skipping to change at page 5, line 16 skipping to change at page 5, line 8
above XRD document that refers to Bob's blog. This URL would then be above XRD document that refers to Bob's blog. This URL would then be
presented to you so that you could then visit his blog. presented to you so that you could then visit his blog.
The email client might also note that Bob has published an avatar The email client might also note that Bob has published an avatar
link relation and use that picture to represent Bob inside the email link relation and use that picture to represent Bob inside the email
client. client.
3.2. Retrieving a Person's Contact Information 3.2. Retrieving a Person's Contact Information
Assume you have Alice in your address book, but her phone number Assume you have Alice in your address book, but her phone number
appears to be invalid. You could use Webfinger to find her current appears to be invalid. You could use WebFinger to find her current
phone number and update your address book. phone number and update your address book.
Let's assume you have a web-based address book that you wish to Let's assume you have a web-based address book that you wish to
update. When you instruct the address book to pull Alice's current update. When you instruct the address book to pull Alice's current
contact information, the address book might issue a query like this contact information, the address book might issue a query like this
to get host metadata information for example.com: to get host metadata information for example.com:
GET /.well-known/host-meta.json HTTP/1.1 GET /.well-known/host-meta.json HTTP/1.1
Host: example.com Host: example.com
skipping to change at page 6, line 21 skipping to change at page 6, line 13
{ {
"expires" : "2012-03-13T20:56:11Z", "expires" : "2012-03-13T20:56:11Z",
"subject" : "acct:alice@example.com", "subject" : "acct:alice@example.com",
"links" : "links" :
[ [
{ {
"rel" : "http://webfinger.net/rel/avatar", "rel" : "http://webfinger.net/rel/avatar",
"href" : "http://example.com/~alice/alice.jpg" "href" : "http://example.com/~alice/alice.jpg"
}, },
{ {
"rel" : "http://packetizer.com/rel/vcard", "rel" : "vcard",
"href" : "http://example.com/~alice/alice.vcf" "href" : "http://example.com/~alice/alice.vcf"
} }
] ]
} }
With this response, the address book might see the vcard [16] link With this response, the address book might see the vcard [16] link
relation and use that file to offer you updated contact information. relation and use that file to offer you updated contact information.
3.3. Simplifying the Login Process 3.3. Simplifying the Login Process
OpenID (http://www.openid.net) is great for allowing users to log OpenID (http://www.openid.net) is great for allowing users to log
into a web site, though one criticism is that it is challenging for into a web site, though one criticism is that it is challenging for
users to remember the URI they are assigned. Webfinger can help users to remember the URI they are assigned. WebFinger can help
address this issue by allowing users to use user@domain-style address this issue by allowing users to use user@domain-style
addresses. Using a user's account URI, a web site can perform a addresses. Using a user's account URI, a web site can perform a
query to discover the associated OpenID identifier for a user. query to discover the associated OpenID identifier for a user.
Let's assume Carol is trying to use OpenID to log into a blog. The Let's assume Carol is trying to use OpenID to log into a blog. The
blog server might issue the following query to get the host metadata blog server might issue the following query to get the host metadata
information: information:
GET /.well-known/host-meta.json HTTP/1.1 GET /.well-known/host-meta.json HTTP/1.1
Host: example.com Host: example.com
skipping to change at page 7, line 49 skipping to change at page 7, line 42
] ]
} }
At this point, the blog server knows that Carol's OpenID identifier At this point, the blog server knows that Carol's OpenID identifier
is https://openid.example.com/carol and could then proceed with the is https://openid.example.com/carol and could then proceed with the
login process as usual. login process as usual.
3.4. Retrieving Device Information 3.4. Retrieving Device Information
While the examples thus far have been focused on information about While the examples thus far have been focused on information about
humans, Webfinger does not limit queries to only those that use the humans, WebFinger does not limit queries to only those that use the
account URI scheme. Let's suppose there are devices on the network account URI scheme. Let's suppose there are devices on the network
like printers and you would like to check the current toner level for like printers and you would like to check the current toner level for
a particular printer identified via the URI like a particular printer identified via the URI like
device:p1.example.com. While the "device" URI scheme is not device:p1.example.com. While the "device" URI scheme is not
presently specified, we use it here for illustrative purposes. presently specified, we use it here for illustrative purposes.
Following the procedures similar to those above, a query may be Following the procedures similar to those above, a query may be
issued to get link relations specific to this URI like this: issued to get link relations specific to this URI like this:
GET /lrdd/?format=json&uri=device%3Ap1.example.com HTTP/1.1 GET /lrdd/?format=json&uri=device%3Ap1.example.com HTTP/1.1
skipping to change at page 8, line 37 skipping to change at page 8, line 29
} }
] ]
} }
While this example is entirely fictitious, you can imagine that While this example is entirely fictitious, you can imagine that
perhaps the Transport Independent, Printer/System Interface [18] may perhaps the Transport Independent, Printer/System Interface [18] may
be enhanced with a web interface that allows a device that be enhanced with a web interface that allows a device that
understands the TIP/SI web interface specification to query the understands the TIP/SI web interface specification to query the
printer for toner levels. printer for toner levels.
4. Webfinger Protocol 4. WebFinger Protocol
Webfinger does not actually introduce a new protocol, per se. WebFinger does not actually introduce a new protocol, per se.
Rather, it builds upon the existing Web Host Metadata [9] Rather, it builds upon the existing Web Host Metadata [9]
specification and leverages the Cross-Origin Resource Sharing (CORS) specification and leverages the Cross-Origin Resource Sharing (CORS)
[7] specification. [7] specification.
4.1. Performing a Webfinger Query 4.1. Performing a WebFinger Query
The first step a client must perform in executing a Webfinger query The first step a client must perform in executing a WebFinger query
is to query for the host metadata using HTTPS or HTTP. The is to query for the host metadata using HTTPS or HTTP. The
procedures are defined in the Web Host Metadata [9] specification. procedures are defined in the Web Host Metadata [9] specification.
Webfinger clients MUST locate the LRDD link relation, if present, and WebFinger clients MUST locate the LRDD link relation, if present, and
perform a query for that link relation, if present. All other link perform a query for that link relation, if present. All other link
templates found must be processed to form a complete resource templates found must be processed to form a complete resource
descriptor. The processing rules in Section 4.2 of RFC 6415 MUST be descriptor. The processing rules in Section 4.2 of RFC 6415 MUST be
followed. followed.
Webfinger servers MUST accept requests for both XRD [8] and JRD [9] WebFinger servers MUST accept requests for both XRD [8] and JRD [9]
documents. The default representation returned by the server MUST be documents. The default representation returned by the server MUST be
an XRD document, but a JRD document MUST be returned if the client an XRD document, but a JRD document MUST be returned if the client
explicitly requests it by using /.well-known/host-meta.json or explicitly requests it by using /.well-known/host-meta.json or
includes an Accept header in the HTTP request with a type of includes an Accept header in the HTTP request with a type of
"application/json" [4]. "application/json" [4].
If the client requests a JRD document when querying for host If the client requests a JRD document when querying for host
metadata, the Webfinger server can assume that the client will want a metadata, the WebFinger server can assume that the client will want a
JRD documents when querying the LRDD resource. As such, when the JRD documents when querying the LRDD resource. As such, when the
Webfinger server returns a JRD document containing host metadata it WebFinger server returns a JRD document containing host metadata it
should include a URI for an LRDD resource that can return a JRD should include a URI for an LRDD resource that can return a JRD
document and MAY include a URI for an LRDD resource that will return document and MAY include a URI for an LRDD resource that will return
an XRD document. an XRD document.
If the client queries the LRDD resource and provides a URI for which If the client queries the LRDD resource and provides a URI for which
the server has no information, the server MUST return a 404 status the server has no information, the server MUST return a 404 status
code. Likewise, any query to a URI in the resource descriptor that code. Likewise, any query to a URI in the resource descriptor that
is unknown to the server should result in the server returning a 404 is unknown to the server MUST result in the server returning a 404
status code. status code.
WebFinger servers MAY include cache validators in a response to
enable conditional requests by clients and/or expiration times as per
RFC 2616 section 13.
4.2. The Web Host Metadata "resource" Parameter 4.2. The Web Host Metadata "resource" Parameter
In addition to the normal processing logic for processing host In addition to the normal processing logic for processing host
metadata information, Webfinger defines the "resource" parameter for metadata information, WebFinger defines the "resource" parameter for
querying for host metadata and returning all of the link relations querying for host metadata and returning all of the link relations
from LRDD and other resource-specific link templates in a single from LRDD and other resource-specific link templates in a single
query. This resource essentially pushes the work to the server to query. This resource essentially pushes the work to the server to
form a complete resource descriptor for the specified resource. form a complete resource descriptor for the specified resource.
Note that support for the "resource" parameter is optional, but Note that support for the "resource" parameter is optional, but
strongly RECOMMENDED for improved performance. If a server does not strongly RECOMMENDED for improved performance. If a server does not
implement the "resource" parameter, then the server's host metadata implement the "resource" parameter, then the server's host metadata
processing logic remains unchanged from RFC 6415. processing logic remains unchanged from RFC 6415.
To utilize the host-meta "resource" parameter, a Webfinger client To utilize the host-meta "resource" parameter, a WebFinger client
issues a request to /.well-known/host-meta or /.well-known/host- issues a request to /.well-known/host-meta or /.well-known/host-
meta.json as usual, but then appends a "resource" parameter as shown meta.json as usual, but then appends a "resource" parameter as shown
in this example: in this example:
GET /.well-known/host-meta.json?resource=\ GET /.well-known/host-meta.json?resource=\
acct%3Abob%40example.com HTTP/1.1 acct%3Abob%40example.com HTTP/1.1
Host: example.com Host: example.com
Note that the "\" character shown above is to indicate that the line Note that the "\" character shown above is to indicate that the line
breaks at this point and continues on the next line. This was shown breaks at this point and continues on the next line. This was shown
only to avoid line wrapping in this document and is not a part of the only to avoid line wrapping in this document and is not a part of the
HTTP protocol. HTTP protocol.
When processing this request, the Webfinger server MUST When processing this request, the WebFinger server MUST
* Return a 404 status code if the URI provided in the resource * Return a 404 status code if the URI provided in the resource
parameter is unknown to the server; and parameter is unknown to the server; and
* Set the "Subject" returned in the response to the value of the * Set the "Subject" returned in the response to the value of the
"resource" parameter if the URI provided in the resource "resource" parameter if the URI provided in the resource
parameter is known to the server parameter is known to the server
The Webfinger client can verify support for the "resource" parameter The WebFinger client can verify support for the "resource" parameter
by checking the value of the Subject returned in the response. If by checking the value of the Subject returned in the response. If
the Subject matches the value of the "resource" parameter, then the the Subject matches the value of the "resource" parameter, then the
"resource" parameter is supported by the server. "resource" parameter is supported by the server.
For illustrative purposes, the following is an example usage of the For illustrative purposes, the following is an example usage of the
"resource" parameter that aligns with the example in Section 1.1.1 of "resource" parameter that aligns with the example in Section 1.1.1 of
RFC 6415. The Webfinger client would issue this request: RFC 6415. The WebFinger client would issue this request:
GET /.well-known/host-meta.json?resource=\ GET /.well-known/host-meta.json?resource=\
http%3A%2F%2Fexample.com%2Fxy HTTP/1.1 http%3A%2F%2Fexample.com%2Fxy HTTP/1.1
Host: example.com Host: example.com
The Webfinger server would reply with this response: The WebFinger server would reply with this response:
HTTP/1.1 200 OK HTTP/1.1 200 OK
Access-Control-Allow-Origin: * Access-Control-Allow-Origin: *
Content-Type: application/json; charset=UTF-8 Content-Type: application/json; charset=UTF-8
{ {
"subject" : "http://example.com/xy", "subject" : "http://example.com/xy",
"properties" : "properties" :
{ {
"http://spec.example.net/color" : "red" "http://spec.example.net/color" : "red"
skipping to change at page 11, line 14 skipping to change at page 11, line 9
"href" : "http://example.com/john" "href" : "http://example.com/john"
}, },
{ {
"rel" : "author", "rel" : "author",
"template" : "http://example.com/author?\ "template" : "http://example.com/author?\
q=http%3A%2F%2Fexample.com%2Fxy" q=http%3A%2F%2Fexample.com%2Fxy"
} }
] ]
} }
4.3. The Web Host Metadata "rel" Parameter
WebFinger also defines the "rel" parameter for use when querying for
host metadata. It is used to return 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
space-separated list of link relations provided via "rel" are
included in the list of links returned in resource descriptor. All
other information normally present in a resource descriptor is
present in the resource descriptor, even when "rel" is employed.
The purpose of the "rel" parameter is to return a subset of
resource's link relations. It is not intended to reduce the work
required of a server to produce a response. That said, 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 support is
RECOMMENDED for both the host-meta resource and the LRDD resource.
For illustrative purposes, the following is an example usage of the
"rel" parameter that aligns with the example in Section 1.1.1 of RFC
6415. The WebFinger client would issue this request to receive links
that are of the type "hub" and "copyright":
GET /.well-known/host-meta.json?resource=\
http%3A%2F%2Fexample.com%2Fxy&rel=hub%20copyright HTTP/1.1
Host: example.com
The WebFinger server would reply with this response:
HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Content-Type: application/json; charset=UTF-8
{
"subject" : "http://example.com/xy",
"properties" :
{
"http://spec.example.net/color" : "red"
},
"links" :
[
{
"rel" : "hub",
"href" : "http://example.com/hub"
},
{
"rel" : "hub",
"href" : "http://example.com/another/hub"
}
]
}
Note that in this example, the "author" links are removed, though all
other content is present. Since there were no "copyright" links,
none are returned.
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, void of any links. When a JRD is returned, the "links"
array MAY be either absent or empty. 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., as indicated via the
"resource" parameter) does not exist.
5. The "acct" URI 5. The "acct" URI
The Web Host Metadata specification [9] allows for any kind of The Web Host Metadata specification [9] allows for any kind of
resource to be queried, as does Webfinger. However, a specific type resource to be queried, as does WebFinger. However, a specific type
of resource is needed in order to query information about a human of resource is needed in order to query information about a human
user. user.
Webfinger uses the "acct" URI to refer to a human user's account on WebFinger uses the "acct" URI to refer to a human user's account on
the Internet. While other URI scheme MAY be used to query for the Internet. While other URI scheme MAY be used to query for
information related to a human user, other schemes are not explicitly information related to a human user, other schemes are not explicitly
defined for that purpose. defined for that purpose.
5.1. Using the "acct" URI 5.1. Using the "acct" URI
The "acct" URI takes a familiar form in looking like an email The "acct" URI takes a familiar form in looking like an email
address. However, the account URI is not an email address and should address. However, the account URI is not an email address and should
not be mistaken for one. Quite often, the account URI minus the not be mistaken for one. Quite often, the account URI minus the
"acct:" scheme prefix may be exactly the same as the user's email "acct:" scheme prefix may be exactly the same as the user's email
address. address.
A user MUST NOT be required to enter the "acct" URI scheme name along A user MUST NOT be required to enter the "acct" URI scheme name along
with his account identifier into any Webfinger client. Rather, the with his account identifier into any WebFinger client. Rather, the
Webfinger client MUST accept identifiers that are void of the "acct:" WebFinger client MUST accept identifiers that are void of the "acct:"
portion of the identifier. Composing a properly formatted "acct" URI portion of the identifier. Composing a properly formatted "acct" URI
is the responsibility of the Webfinger client. is the responsibility of the WebFinger client.
A user MAY provide a fully-specified "acct" URI. A user MAY provide a fully-specified "acct" URI.
5.2. Syntax of "acct" URI 5.2. Syntax of "acct" URI
The "acct" URI syntax is defined here in Augmented Backus-Naur Form The "acct" URI syntax is defined here in Augmented Backus-Naur Form
(ABNF) [6] and borrows syntax elements from RFC 3986 [5]: (ABNF) [6] and borrows syntax elements from RFC 3986 [5]:
acctURI = "acct:" userpart "@" domainpart acctURI = "acct:" userpart "@" domainpart
userpart = 1*( unreserved / pct-encoded ) userpart = 1*( unreserved / pct-encoded )
skipping to change at page 12, line 29 skipping to change at page 13, line 44
Section 3 of RFC 3987 [13]. Section 3 of RFC 3987 [13].
6. The "acct" Link Relation 6. The "acct" Link Relation
6.1. Purpose for the "acct" Link Relation 6.1. Purpose for the "acct" Link Relation
Users of some services might have an "acct" URI that looks Users of some services might have an "acct" URI that looks
significantly different from his or her email address, perhaps using significantly different from his or her email address, perhaps using
an entirely different domain name. It is also possible for a user an entirely different domain name. It is also possible for a user
have multiple accounts that a user wants to advertise and that a have multiple accounts that a user wants to advertise and that a
Webfinger client may want to query. To address both of these needs, WebFinger client may want to query. To address both of these needs,
this specification defines the "acct" link relation. this specification defines the "acct" link relation.
Since an account may make a reference to one or more different Since an account may make a reference to one or more different
accounts, Webfinger clients MUST take steps to avoid loops wherein accounts, WebFinger clients MUST take steps to avoid loops wherein
two accounts, directly or indirectly, refer the client to each other. two accounts, directly or indirectly, refer the client to each other.
There are no limits on the number of "acct" link relations that might There are no limits on the number of "acct" link relations that might
be returned in a Webfinger query. be returned in a WebFinger query.
An "acct" link relation used within the context of a Webfinger query An "acct" link relation used within the context of a WebFinger query
for a user's account MUST NOT return "acct" link relations for for a user's account MUST NOT return "acct" link relations for
another individual. another individual.
The "acct" link relation also makes it possible to use the link The "acct" link relation also makes it possible to use the link
relation in HTML documents or in HTTP headers as described in the Web relation in HTML documents or in HTTP headers as described in the Web
Linking specification [3]. This would allow, by way of example, for Linking specification [3]. This would allow, by way of example, for
a user to advertise his or her account identifier in a blog, article, a user to advertise his or her account identifier in a blog, article,
or other content located on a server that is unrelated to his user or other content located on a server that is unrelated to his user
account. Since there may be multiple contributors to an article, account. Since there may be multiple contributors to an article,
there may be more than one "acct" link relation in an HTML document there may be more than one "acct" link relation in an HTML document
skipping to change at page 13, line 14 skipping to change at page 14, line 30
from within a user's account, as described in the preceding from within a user's account, as described in the preceding
paragraphs. paragraphs.
6.2. Example Message Exchange Using the "acct" Link Relation 6.2. Example Message Exchange Using the "acct" Link Relation
Consider the following non-normative example. Consider the following non-normative example.
Suppose Alice receives an email from bob@example.net. While Bob's Suppose Alice receives an email from bob@example.net. While Bob's
email identifier might be in the example.net domain, he holds his email identifier might be in the example.net domain, he holds his
account with an "acct" URI in the example.com domain. His email account with an "acct" URI in the example.com domain. His email
provider may provide Webfinger services to enable redirecting Alice provider may provide WebFinger services to enable redirecting Alice
when she queries for acct:bob@example.net. when she queries for acct:bob@example.net.
Suppose Alice's client issues the following request: Suppose Alice's client issues the following request:
GET /.well-known/host-meta.json?resource=\ GET /.well-known/host-meta.json?resource=\
acct%3Abob%40example.net HTTP/1.1 acct%3Abob%40example.net HTTP/1.1
Host: example.net Host: example.net
The response that Alice's client receives back might be: The response that Alice's client receives back might be:
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"rel" : "acct", "rel" : "acct",
"href" : "acct:bob@example.com" "href" : "acct:bob@example.com"
}, },
{ {
"rel" : "acct", "rel" : "acct",
"href" : "acct:bob@example.org" "href" : "acct:bob@example.org"
} }
] ]
} }
Alice's Webfinger client could then perform queries against the URIs Alice's WebFinger client could then perform queries against the URIs
acct:bob@example.com and acct:bob@example.org in order to get the acct:bob@example.com and acct:bob@example.org in order to get the
information Alice is seeking. information Alice is seeking.
7. Cross-Origin Resource Sharing (CORS) 7. Cross-Origin Resource Sharing (CORS)
Webfinger is most useful when it is accessible without restrictions WebFinger is most useful when it is accessible without restrictions
on the Internet, and that includes web browsers. Therefore, on the Internet, and that includes web browsers. Therefore,
Webfinger servers MUST support Cross-Origin Resource Sharing (CORS) WebFinger servers MUST support Cross-Origin Resource Sharing (CORS)
[7]. Specifically, all queries to /.well-known/host-meta, /.well- [7]. Specifically, all queries to /.well-known/host-meta, /.well-
known/host-meta.json, and to the LRDD URI must include the following known/host-meta.json, and to the LRDD URI must include the following
HTTP header in the response: HTTP header in the response:
Access-Control-Allow-Origin: * Access-Control-Allow-Origin: *
8. Security Considerations 8. Security Considerations
All of the security considerations applicable to Web Host Metadata All of the security considerations applicable to Web Host Metadata
[9] and Cross-Origin Resource Sharing [7] are also applicable to this [9] and Cross-Origin Resource Sharing [7] are also applicable to this
specification. Of particular importance is the recommended use of specification. Of particular importance is the recommended use of
HTTPS to ensure that information is not modified during transit. HTTPS to ensure that information is not modified during transit.
Clients should verify that the certificate used on an HTTPS Clients should verify that the certificate used on an HTTPS
connection is valid. connection is valid.
When using HTTP to request an XRD document, Webfinger clients SHOULD When using HTTP to request an XRD document, WebFinger clients SHOULD
verify the XRD document's signature, if present, to ensure that the verify the XRD document's signature, if present, to ensure that the
XRD document has not been modified. Webfinger servers SHOULD include XRD document has not been modified. WebFinger servers SHOULD include
a signature for XRD documents. a signature for XRD documents.
Service providers and users should be aware that placing information Service providers and users should be aware that placing information
on the Internet accessible through Webfinger means that any user can on the Internet accessible through WebFinger means that any user can
access that information. While Webfinger can be an extremely useful access that information. While WebFinger can be an extremely useful
tool for allowing quick and easy access to one's avatar, blog, or tool for allowing quick and easy access to one's avatar, blog, or
other personal information, users should understand the risks, too. other personal information, users should understand the risks, too.
If one does not wish to share certain information with the world, do If one does not wish to share certain information with the world, do
not allow that information to be accessible through Webfinger. not allow that information to be accessible through WebFinger.
The aforementioned word of caution is perhaps worth emphasizing again The aforementioned word of caution is perhaps worth emphasizing again
with respect to dynamic information one might wish to share, such as with respect to dynamic information one might wish to share, such as
the current location of a user. Webfinger can be a powerful tool the current location of a user. WebFinger can be a powerful tool
used to assemble information about a person all in one place, but used to assemble information about a person all in one place, but
service providers and users should be mindful of the nature of that service providers and users should be mindful of the nature of that
information shared and the fact that it might be available for the information shared and the fact that it might be available for the
entire world to see. Sharing location information, for example, entire world to see. Sharing location information, for example,
would potentially put a person in danger from any individual who would potentially put a person in danger from any individual who
might seek to inflict harm on that person. might seek to inflict harm on that person.
The easy access to user information via Webfinger was a design goal 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 of the protocol, not a limitation. If one wishes to limit access to
information available via Webfinger, such as a Webfinger server for information available via WebFinger, such as a WebFinger server for
use inside a corporate network, the network administrator must take use inside a corporate network, the network administrator must take
measures necessary to limit access from outside the network. measures necessary to limit access from outside the network.
9. IANA Considerations 9. IANA Considerations
RFC Editor: Please replace QQQQ in the following two sub-sections RFC Editor: Please replace QQQQ in the following two sub-sections
with a reference to this RFC. with a reference to this RFC.
9.1. Registration of the "acct" URI scheme name 9.1. Registration of the "acct" URI scheme name
skipping to change at page 15, line 26 skipping to change at page 16, line 40
URI scheme syntax: see Section 4.1 of RFC QQQQ URI scheme syntax: see Section 4.1 of RFC QQQQ
URI scheme semantics: see Section 4.1 of RFC QQQQ URI scheme semantics: see Section 4.1 of RFC QQQQ
Encoding considerations: The "acct" URI scheme allows any character Encoding considerations: The "acct" URI scheme allows any character
from the Unicode character set encoded as a UTF-8 string that is from the Unicode character set encoded as a UTF-8 string that is
then percent-encoded as necessary to result in an internal then percent-encoded as necessary to result in an internal
representation in US-ASCII [10] representation in US-ASCII [10]
Applications/protocols that use this URI scheme name: Webfinger Applications/protocols that use this URI scheme name: WebFinger
Security considerations: see Section 7 of RFC QQQQ Security considerations: see Section 7 of RFC QQQQ
Contact: Gonzalo Salgueiro <gsalguei@cisco.com> Contact: Gonzalo Salgueiro <gsalguei@cisco.com>
Author/Change controller: IETF <ietf@ietf.org> Author/Change controller: IETF <ietf@ietf.org>
References: See Section 10 of RFC QQQQ References: See Section 10 of RFC QQQQ
9.2. Registration of the "acct" Link Relation Type 9.2. Registration of the "acct" Link Relation Type
Relation Name: acct Relation Name: acct
Description: A link relation that refers to a user's WebFinger
Description: A link relation that refers to a user's Webfinger
account identifier. account identifier.
Reference: RFC QQQQ Reference: RFC QQQQ
Notes: Notes:
Application Data: Application Data:
10. Acknowledgments 10. Acknowledgments
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2011. 2011.
[17] Internet Assigned Numbers Authority (IANA) Registry, "Uniform [17] Internet Assigned Numbers Authority (IANA) Registry, "Uniform
Resource Identifier (URI) Schemes", Resource Identifier (URI) Schemes",
<http://www.iana.org/assignments/uri-schemes.html>. <http://www.iana.org/assignments/uri-schemes.html>.
[18] "Transport Independent, Printer/System Interface", IEEE Std [18] "Transport Independent, Printer/System Interface", IEEE Std
1284.1-1997, 1997. 1284.1-1997, 1997.
[19] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC [19] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
2279, November 2003. 3629, November 2003.
[20] Information Systems -- Coded Character Sets 7-Bit American [20] Information Systems -- Coded Character Sets 7-Bit American
National Standard Code for Information Interchange (7-Bit National Standard Code for Information Interchange (7-Bit
ASCII), ANSI X3.4-1986, December 30, 1986. ASCII), ANSI X3.4-1986, December 30, 1986.
[21] Hoffman, P., Yergeau, F., "UTF-16, an encoding of ISO 10646", [21] Hoffman, P., Yergeau, F., "UTF-16, an encoding of ISO 10646",
RFC 2781, February 2000. RFC 2781, February 2000.
Author's Addresses Author's Addresses
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IM: xmpp:gsalguei@cisco.com IM: xmpp:gsalguei@cisco.com
Joseph Smarr Joseph Smarr
Google Google
Email: jsmarr@google.com Email: jsmarr@google.com
Change Log (To Be Deleted Before Publication) Change Log (To Be Deleted Before Publication)
============================================= =============================================
-03 Draft
* Changed the name from Webfinger to WebFinger (common usage)
* Added a new paragraph to Section 4.1 to remind readers that WebFinger
benefits from all of the existing HTTP caching functionality
* Added the "rel" parameter to allow filtering the results of a
WebFinger query to include Links of the specified type(s)
* Corrected a reference to an obsoleted RFC
* Removed extraneous text from the terminology section
-02 Draft -02 Draft
* Minor editorial changes * Minor editorial changes
* Added <Expires/> to the XML example to highlight that this element * Added <Expires/> to the XML example to highlight that this element
exists, since some may not be aware exists, since some may not be aware
* Changed some of the link relation values, particularly for those that * Changed some of the link relation values, particularly for those that
are not yet standardized are not yet standardized
* Added a note about "device:" not being standard * Added a note about "device:" not being standard
* Overhauled the "acct" link relation text, breaking the normative and * Overhauled the "acct" link relation text, breaking the normative and
non-normative pieces apart non-normative pieces apart
* Added additional text to the security considerations section related * Added additional text to the security considerations section related
to dynamic information (e.g., geographic information) to dynamic information (e.g., geographic information)
 End of changes. 65 change blocks. 
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