One document matched: draft-nottingham-http-new-status-01.txt
Differences from draft-nottingham-http-new-status-00.txt
Network Working Group M. Nottingham
Internet-Draft
Updates: 2616 (if approved) R. Fielding
Intended status: Standards Track Adobe
Expires: February 14, 2012 August 13, 2011
Additional HTTP Status Codes
draft-nottingham-http-new-status-01
Abstract
This document specifies additional HyperText Transfer Protocol (HTTP)
status codes for a variety of common situations.
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 February 14, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. 428 Network Authentication Required . . . . . . . . . . . . . . 3
3.1. The 428 Status Code and Captive Portals . . . . . . . . . . 3
4. 429 Limit Exceeded . . . . . . . . . . . . . . . . . . . . . . 4
5. 431 Request Header Fields Too Large . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6.1. 428 Network Authentication Required . . . . . . . . . . . . 6
6.2. 429 Limit Exceeded . . . . . . . . . . . . . . . . . . . . 6
6.3. 431 Request Header Fields Too Large . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
Appendix A. Issues Raised by Captive Portals . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
This document specifies additional HTTP [RFC2616] status codes for a
variety of common situations, to improve interoperability and avoid
confusion when other, less precise status codes are used.
Feedback should occur on the ietf-http-wg@w3.org mailing list,
although this draft is NOT a work item of the IETF HTTPbis Working
Group.
2. Requirements
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 [RFC2119].
3. 428 Network Authentication Required
This status code indicates that the client needs to authenticate to
gain network access.
The response representation SHOULD indicate how to do this; e.g.,
with an HTML form for submitting credentials.
The 428 status SHOULD NOT be generated by origin servers; it is
intended for use by intermediaries.
Responses with the 428 status code MUST NOT be stored by a cache.
3.1. The 428 Status Code and Captive Portals
This section demonstrates a typical use of the 428 status code; it is
not normative. See Appendix A for an explanation of the issues that
motivate this status code.
A network operator wishing to require some authentication, acceptance
of terms or other user interaction before granting access usually
does so by identify clients who have not done so ("unknown clients")
using their MAC addresses.
Unknown clients then have all traffic blocked, except for that on TCP
port 80, which is sent to a HTTP server (the "login server")
dedicated to "logging in" unknown clients, and of course traffic to
the login server itself.
For example, a user agent might connect to a network and make the
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following HTTP request on TCP port 80:
GET /index.htm HTTP/1.1
Host: www.example.com
Upon receiving such a request, the login server would generate a 428
response:
HTTP/1.1 428 Network Authentication Required
Refresh: 0; url=https://login.example.net/
Content-Type: text/html
<html>
<head>
<title>Network Authentication Required</title>
</head>
<body>
<h1>You are being redirected to log into the network...</h1>
</body>
</html>
Here, the 428 status code assures that non-browser clients will not
interpret the response as being from the origin server, and the
Refresh header redirects the user agent to the login server (an HTML
META element can be used for this as well).
Note that the 428 response can itself contain the login interface,
but it may not be desirable to do so, because browsers would show the
login interface as being associated with the originally requested
URL, which may cause confusion.
4. 429 Limit Exceeded
This status code indicates that the client has exceeded some usage
limit on the origin server, such as sending too many requests in a
given amount of time ("rate limiting").
The response representations SHOULD include details explaining the
limit, and MAY include a Retry-After header indicating how long to
wait before making a new request.
For example:
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HTTP/1.1 429 Limit Exceeded
Content-Type: text/html
Retry-After: 3600
<html>
<head>
<title>Limit Exceeded</title>
</head>
<body>
<h1>Limit Exceeded</h1>
<p>I only allow 50 requests per hour to this Web site.
Try again soon.</p>
</body>
</html>
Note that this specification does not define specific limits, nor
their scope. For example, an origin server that is limiting request
rates can do so based upon counts of requests on a per-resource
basis, across the entire server, or even among a set of servers.
Responses with the 429 status code MUST NOT be stored by a cache.
5. 431 Request Header Fields Too Large
This status code indicates that the server is unwilling to process
the request because its header fields are too large. The request MAY
be resubmitted after reducing the size of the request header fields.
It can be used both when the set of request header fields in total
are too large, and when a single header field is at fault. In the
latter case, the response representation SHOULD specify which header
field was too large.
For example:
HTTP/1.1 431 Request Header Fields Too Large
Content-Type: text/html
<html>
<head>
<title>Request Header Fields Too Large</title>
</head>
<body>
<h1>Request Header Fields Too Large</h1>
<p>The "Example" header was too large.</p>
</body>
</html>
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Responses with the 431 status code MUST NOT be stored by a cache.
6. Security Considerations
6.1. 428 Network Authentication Required
In common use, a response carrying the 428 status code will not come
from the origin server indicated in the request's URL. This presents
many security issues; e.g., an attacking intermediary may be
inserting cookies into the original domain's name space, may be
observing cookies or HTTP authentication credentials sent from the
user agent, and so on.
However, these risks are not unique to the 428 status code; in other
words, a captive portal that is not using this status code introduces
the same issues.
6.2. 429 Limit Exceeded
Servers are not required to use the 429 status code; when limiting
resource usage, it may be more appropriate to just drop connections,
or take other steps.
6.3. 431 Request Header Fields Too Large
Servers are not required to use the 431 status code; when under
attack, it may be more appropriate to just drop connections, or take
other steps.
7. IANA Considerations
The HTTP Status Codes Registry should be updated with the following
entries:
o Code: 428
o Description: Network Authentication Required
o Specification: [ this document ]
o Code: 429
o Description: Limit Exceeded
o Specification: [ this document ]
o Code: 431
o Description: Request Header Fields Too Large
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o Specification: [ this document ]
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
8.2. Informative References
[RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault,
"Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
March 2007.
[RFC4918] Dusseault, L., "HTTP Extensions for Web Distributed
Authoring and Versioning (WebDAV)", RFC 4918, June 2007.
Appendix A. Issues Raised by Captive Portals
Since clients cannot differentiate between a portal's response and
that of the HTTP server that they intended to communicate with, a
number of issues arise.
One example is the "favicon.ico"
<http://en.wikipedia.org/wiki/Favicon> commonly used by browsers to
identify the site being accessed. If the favicon for a given site is
fetched from a captive portal instead of the intended site (e.g.,
because the user is unauthenticated), it will often "stick" in the
browser's cache (most implementations cache favicons aggressively)
beyond the portal session, so that it seems as if the portal's
favicon has "taken over" the legitimate site.
Another browser-based issue comes about when P3P
<http://www.w3.org/TR/P3P/> is supported. Depending on how it is
implemented, it's possible a browser might interpret a portal's
response for the p3p.xml file as the server's, resulting in the
privacy policy (or lack thereof) advertised by the portal being
interpreted as applying to the intended site. Other Web-based
protocols such as WebFinger
<http://code.google.com/p/webfinger/wiki/WebFingerProtocol>, CORS
<http://www.w3.org/TR/cors/> and OAuth
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<http://tools.ietf.org/html/draft-ietf-oauth-v2> may also be
vulnerable to such issues.
Although HTTP is most widely used with Web browsers, a growing number
of non-browsing applications use it as a substrate protocol. For
example, WebDAV [RFC4918] and CalDAV [RFC4791] both use HTTP as the
basis (for network filesystem access and calendaring, respectively).
Using these applications from behind a captive portal can result in
spurious errors being presented to the user, and might result in
content corruption, in extreme cases.
Similarly, other non-browser applications using HTTP can be affected
as well; e.g., widgets <http://www.w3.org/TR/widgets/>, software
updates, and other specialised software such as Twitter clients and
the iTunes Music Store.
It should be noted that it's sometimes believed that using HTTP
redirection to direct traffic to the portal addresses these issues.
However, since many of these uses "follow" redirects, this is not a
good solution.
Authors' Addresses
Mark Nottingham
Email: mnot@mnot.net
URI: http://www.mnot.net/
Roy T. Fielding
Adobe Systems Incorporated
345 Park Ave
San Jose, CA 95110
USA
Email: fielding@gbiv.com
URI: http://roy.gbiv.com/
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