One document matched: draft-nottingham-http-portal-02.xml

<?xml version="1.0" encoding="utf-8"?>

<!DOCTYPE rfc SYSTEM "../xml2rfc/rfc2629.dtd" [
<!ENTITY rfc2119 SYSTEM '../bibxml/reference.RFC.2119.xml'>      
]>

<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
<?rfc toc="yes" ?>
<?rfc tocdepth="3" ?>
<?rfc tocindent="yes" ?>
<?rfc symrefs="yes" ?>
<?rfc sortrefs="yes"?>
<?rfc iprnotified="no" ?>
<?rfc strict="yes" ?>
<?rfc compact="yes" ?>
<?rfc comments="yes" ?>
<?rfc inline="yes" ?>

<rfc ipr="trust200902" docName="draft-nottingham-http-portal-02" category="std">
   <front>
      <title abbrev="Network Authentication Required">The Network Authentication Required HTTP Status Code</title>
      <author initials="M." surname="Nottingham" fullname="Mark Nottingham">
         <organization></organization>
         <address>       
            <email>mnot@mnot.net</email> 
            <uri>http://www.mnot.net/</uri>       
         </address>
      </author>
      <date year="2011"/>
      <abstract>
         <t>"Captive portals" are a commonly-deployed means of obtaining
         access credentials and/or payment for a network. This memo introduces
         a new HTTP status code as a means of addressing issues found in these
         deployments.</t>
         
         <t>This memo should be discussed on the ietf-http-wg@w3.org mailing
         list, although it is not a work item of the HTTPbis WG.</t>
      </abstract>
   </front>

   <middle>

      <section title="Introduction">
      
         <t>It has become common for networks to require authentication,
         payment and/or acceptance of terms of service before granting access.
         Typically, this occurs when accessing "public" networks such as those
         in hotels, trains, conference centres and similar networks.</t>
      
         <t>While there are several potential means of providing credentials
         to a network, these are not yet universally supported, and in some
         instances the network administrator requires that information (e.g.,
         terms of service, login information) be displayed to end users.</t>
      
         <t>In such cases, it has become widespread practice to use a "captive
         portal" that diverts HTTP requests to the administrator's web page.
         Once the user has satisfied requirements (e.g., for payment,
         acceptance of terms), the diversion is ended and "normal" access to
         the network is allowed.</t>
      
         <t>Typically, this diversion is accomplished by one of several
         possible techniques; 
            <list style="symbols">
               <t>IP interception - all requests on port 80 are intercepted
               and send to the portal.</t>
               <t>HTTP redirects - all requests on port 80 are intercepted and
               an HTTP redirect to the portal's URL is returned.</t>
               <t>DNS interception - all DNS lookups return the portal's IP
               address.</t>
            </list> 
         </t>
      
         <t>In each case, the intent is that users connecting to the network
         will open a Web browser and see the portal.</t>
         
         <t>However, because port 80 is used for non-browser traffic, a number
         of issues (see <xref target="issues"/>) have been encountered.</t>

         <t>This memo introduces a new HTTP status code, 428 Network
         Authentication Required, as a solution to some of these issues. <xref
         target="use"/> outlines how it might be used in typical
         deployments.</t>

      </section>


      <section title="428 Network Authentication Required" anchor="status-code">
      
         <t>This status code indicates that the client should authenticate to
         gain network access before resubmitting the request.</t>
         
         <t>The response body SHOULD indicate how to do this;
         e.g., with an HTML form for submitting credentials.</t>
         
         <t>Responses with the 428 status code MUST NOT be stored by a
         cache.</t>
            
      </section>
      
      <section title="Security Considerations">
         
         <t>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.</t>
         
         <t>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.</t>

      </section>

      <section title="IANA Considerations">

         <t>The HTTP Status Codes Registry should be updated with the
         following entry:</t>

         <t><list style="symbols">
            <t>Code: 428</t>
            <t>Description: Network Authentication Required</t>
            <t>Specification: [ this document ]</t>
         </list></t>

      </section>

   </middle>

   <back>

      <section title="Using the 428 Status Code" anchor="use">
      
         <t>This appendix demonstrates a typical use of the 428 status code;
         it is not normative.</t>
      
         <t>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.</t>
            
         <t>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.</t>
            
         <t>For example, a user agent might connect to a network and make the
         following HTTP request on TCP port 80:</t>
            
         <figure><artwork xml:space="preserve"><![CDATA[            
GET /index.htm HTTP/1.1
Host: www.example.com
User-Agent: ExampleAgent
]]></artwork></figure>

         <t>Upon receiving such a request, the login server would generate a
         428 response:</t>

         <figure><artwork xml:space="preserve"><![CDATA[            
HTTP/1.1 428 Network Authentication Required
Refresh: 0; url=https://login.example.net/
Content-Type: text/html

<html>
   <head>
   </head>
   <body>
      <h1>You are being redirected to log into the network...</h1>
   </body>
</html>
]]></artwork></figure>

         <t>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).</t>
            
         <t>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.</t>
      
      </section>
 
      <section title="Issues Raised by Captive Portals" anchor="issues">

         <t>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.</t>
         
          <t>One example is the "favicon.ico" <eref
         target="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.</t>
         
          <t>Another browser-based issue comes about when P3P <eref
         target="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 <eref
         target="http://code.google.com/p/webfinger/wiki/WebFingerProtocol"/>,
         CORS <eref target="http://www.w3.org/TR/cors/"/> and OAuth <eref
         target="http://tools.ietf.org/html/draft-ietf-oauth-v2"/> may also be
         vulnerable to such issues.</t>
         
          <t>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 <eref
         target="http://tools.ietf.org/html/rfc4918"/> and CalDAV <eref
         target="http://www.ietf.org/rfc/rfc4791.txt"/> 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.</t>
         
          <t>Similarly, other non-browser applications using HTTP can be
         affected as well; e.g., widgets <eref
         target="http://www.w3.org/TR/widgets/"/>, software updates, and other
         specialised software such as Twitter clients and the iTunes Music
         Store.</t>
         
          <t>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.</t>

      </section>

      <section title="Non-HTTP Applications and Techniques">
         
         <t>This memo does not address non-HTTP applications, such as IMAP,
         POP, or even TLS-encapsulated HTTP. Since captive portals almost
         always target Web browsers (has anyone ever seen one that inserts an
         e-mail into your inbox asking you to authenticate?), this is
         appropriate.</t>
         
         <t>Instead, it is anticipated that well-behaved portals will block
         all non-HTTP ports (especially port 443) until the user has
         successfully authenticated.</t>
            
         <t>Overall, there may also be an interesting discussion to be had
         about improving network access methods to the point where a user
         interface can be presented for the same purposes, without resorting
         to intercepting HTTP traffic. However, since such a mechanism would
         by necessity require modifying the network stack and operating system
         of the client, this memo takes a more modest approach.</t>

      </section>

      <section title="Acknowledgements">
         <t>The author takes all responsibility for errors and omissions.</t>
      </section>


   </back>
</rfc>