JEP-0070: Verifying HTTP Requests via XMPP

This document defines a protocol that enables verification of an HTTP request via XMPP.


NOTICE: This JEP is currently within Last Call or under consideration by the Jabber Council for advancement to the next stage in the JSF standards process. For further details, visit <http://www.jabber.org/council/queue.shtml>.


JEP Information

Status: Proposed
Type: Standards Track
Number: 0070
Version: 0.9
Last Updated: 2005-11-09
JIG: Standards JIG
Approving Body: Jabber Council
Dependencies: XMPP Core, RFC 2616, RFC 2617, JEP-0030
Supersedes: None
Superseded By: None
Short Name: http-auth
Wiki Page: <http://wiki.jabber.org/index.php/Verifying HTTP Requests via XMPP (JEP-0070)>

Author Information

Matthew Miller

Email: linuxwolf@outer-planes.net
JID: linuxwolf@outer-planes.net

Joe Hildebrand

Email: jhildebrand@jabber.com
JID: hildjj@jabber.org

Dave Smith

Email: dizzyd@jabber.org
JID: dizzyd@jabber.org

Peter Saint-Andre

Email: stpeter@jabber.org
JID: stpeter@jabber.org

Legal Notice

This Jabber Enhancement Proposal is copyright 1999 - 2005 by the Jabber Software Foundation (JSF) and is in full conformance with the JSF's Intellectual Property Rights Policy <http://www.jabber.org/jsf/ipr-policy.shtml>. This material may be distributed only subject to the terms and conditions set forth in the Creative Commons Attribution License (<http://creativecommons.org/licenses/by/2.5/>).

Discussion Venue

The preferred venue for discussion of this document is the Standards-JIG discussion list: <http://mail.jabber.org/mailman/listinfo/standards-jig>.

Given that this JEP normatively references IETF technologies, discussion on the JSF-IETF list may also be appropriate (see <http://mail.jabber.org/mailman/listinfo/jsf-ietf> for details).

Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) specifications contributed by the Jabber Software Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this JEP has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.

Conformance Terms

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.


Table of Contents

1. Introduction
2. Terminology
2.1. HTTP Terms
2.2. Entities
3. Requirements
4. Use Case
4.1. HTTP Client Sends Request via HTTP
4.2. HTTP Server Sends Authenticate Response via HTTP
4.3. HTTP Client Sends Authorization Request via HTTP
4.3.1. Basic Access Authentication Scheme
4.3.2. Digest Access Authentication Scheme
4.3.3. Additional Authentication Schemes
4.4. HTPP Server Processes Request
4.5. XMPP Server Requests Confirmation via XMPP
4.6. XMPP Client Confirms Request via XMPP
4.7. HTTP Server Allows HTTP Client to Access Object
5. Implementation Notes
5.1. Interaction of HTTP methods
6. Security Considerations
6.1. Association of Request
6.2. Strength of Authentication Schemes
6.3. Channel Encryption
6.4. End-to-End Encryption
7. IANA Considerations
8. Jabber Registrar Considerations
8.1. Protocol Namespaces
9. XML Schema
Notes
Revision History


1. Introduction

HTTP (see RFC 2616 [1]) is a nearly-ubiquitous mechanism for the publication and retrieval of information over the Internet. Sometimes it is appropriate for an HTTP Server to allow access to that information only if the HTTP Client first provides authentication credentials. While there exist several standardized HTTP authentication schemes (see RFC 2617 [2]), it may be useful in some applications to enforce verification of an HTTP request by requiring an XMPP entity (normally an IM user) to confirm that it made the request. This request verification can be combined with native HTTP authentication to provide a stronger association between the request and a particular user, as well as to take advantage of the strong user authentication provided in XMPP (see RFC 3920 [3]).

2. Terminology

2.1 HTTP Terms

This document inherits terminology about the HyperText Transfer Protocol from RFC 2616 and RFC 2617.

2.2 Entities

Table 1: Terms for Entities Described Herein

Term Definition
HTTP Client A client that implements the HyperText Transfer Protocol (HTTP)
HTTP Server A server that implements the HyperText Transfer Protocol (HTTP)
XMPP Client A client that implements the Extensible Messaging and Presence Protocol (XMPP) or its antecedents
XMPP Server A server that implements the Extensible Messaging and Presence Protocol (XMPP) or its antecedents

Note well that an XMPP Client can simultaneously be an HTTP Client (or vice-versa), and that an XMPP Server can simultaneously be an HTTP Server (or vice-versa). However, for the purposes of this discussion, we assume that these entities are logically if not physically separate and distinct.

3. Requirements

The motivations for this document are to:

4. Use Case

The process flow for this protocol is as follows:

  1. HTTP Client requests object via HTTP.
  2. HTTP Server sends Authenticate Response via HTTP.
  3. HTTP Client sends Authorization Request via HTTP (E1).
  4. HTPP Server processes request and forwards it to XMPP Server.
  5. XMPP Server requests confirmation via XMPP (E2).
  6. XMPP Client confirms request via XMPP.
  7. XMPP Server delivers confirmation to HTTP Server.
  8. HTTP Server allows HTTP Client to access object (E3).

Error cases:

This process flow is described in more detail in the following sections.

4.1 HTTP Client Sends Request via HTTP

Let us stipulate that an XMPP user (say, <juliet@capulet.com>) learns of an HTTP URL (e.g., <https://files.shakespeare.lit:9345/missive.html>). The user then attempts to retrieve the URL using her HTTP Client, which opens a TCP connection to the appropriate port of the host and sends an HTTP request as defined in RFC 2616. The request method MAY be any valid HTTP request method, including user-defined methods.

An example is provided below:

Example 1. HTTP Client Makes Request (No Credentials)

GET https://files.shakespeare.lit:9345/missive.html HTTP/1.1
    

In order to avoid a round trip, the initial request MAY contain an HTTP Authorization as described below.

4.2 HTTP Server Sends Authenticate Response via HTTP

If the user did not provide authorization credentials in the initial request, the HTTP Server then MUST respond with a (401) Authenticate response as defined in RFC 2616. The response MUST contain an HTTP 401 error and one WWW-Authenticate header for each authentication scheme recognized by the HTTP Server. In order to provide authentication via XMPP, at least one of these headers MUST specify a realm of "xmpp" (case-sensitive).

Example 2. HTTP Server Returns Autnenticate Response

401 Unauthorized HTTP/1.1
WWW-Authenticate: Basic realm="xmpp"
WWW-Authenticate: Digest realm="xmpp", 
                  domain="files.shakespeare.lit", 
                  stale=false, 
                  nonce="ec2cc00f21f71acd35ab9be057970609", 
                  qop="auth", 
                  algorithm="MD5"
    

4.3 HTTP Client Sends Authorization Request via HTTP

The HTTP Client responds with an Authorization Request as defined in RFC 2616. The following rules apply:

  1. The request MUST include the Jabber Identifier (JID) of the user making the request. This SHOULD be the full JID (<user@host/resource>) of a client that supports the protocol defined herein, although it MAY be the user's bare JID (<user@host>) instead.
  2. The request MUST include a transaction identifier for the request. This identifier MUST be unique within the context of the HTTP Client's interaction with the HTTP Server. If the HTTP request is generated by the XMPP Client (e.g., because the HTTP URL was discovered via Out-of-Band Data [4]) tyhen the transaction identifier SHOULD be generated by the client; if not, the transaction identifier SHOULD be provided by the human user who controls the HTTP Client.

The Authorization Request process is described in the following subsections.

4.3.1 Basic Access Authentication Scheme

The Basic Access Authentication scheme is defined in RFC 2617. This scheme specifies that the authorization information shall consist of a userid and password, separated by a ':' character and then encoded using Base64. When the realm is "xmpp", the profile defined herein further specifies that the userid MUST be a valid JID as described above, that the password entity MUST be a transaction identifier as described above, that Base64 encoding MUST adhere to Section 3 of RFC 3548 [5], and that any character that is outside the range of the US-ASCII coded character set MUST be transformed into a percent-encoded octet as specified in Section 2.1 of RFC 3986 [6].

(Refer to RFC 2617 for specification of the syntax of the Basic Access Authentication scheme; that information is not duplicated here.)

Example 3. HTTP Client Makes Basic Authorization Request

Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
      

4.3.2 Digest Access Authentication Scheme

The Digest Access Authentication scheme is defined in RFC 2617. This scheme specifies that the authorization information shall consist of the MD5 checksum of the username, the password, a nonce value provided in the challenge, the HTTP method, and the requested URI. When the realm is "xmpp", the profile defined herein further specifies that prior to creating the MD5 checksum the username MUST be a valid JID as described above, that the password MUST be a transaction identifier as described above, and that any character that is outside the range of the US-ASCII coded character set MUST be transformed into a percent-encoded octet as specified in Section 2.1 of RFC 3986.

(Refer to RFC 2617 for specification of the syntax of the Digest Access Authentication scheme; that information is not duplicated here.)

Example 4. HTTP Client Makes Digest Authorization Request

Authorization: Digest username="juliet@capulet.com",
               realm="xmpp",
               nonce="ec2cc00f21f71acd35ab9be057970609", 
               uri="missive.html",
               qop=auth,
               nc=00000001,
               cnonce="0a4f113b",
               response="6629fae49393a05397450978507c4ef1",
               opaque="5ccc069c403ebaf9f0171e9517f40e41" 
      

4.3.3 Additional Authentication Schemes

The HTTP Server MAY offer any other valid authentication scheme, instead of or in addition to the Basic and Digest schemes mentioned above, as long as the scheme makes it possible to specify a userid (JID) and transaction identifier as described above. However, it is RECOMMENDED to implement both the Basic and Digest authentication schemes.

4.4 HTPP Server Processes Request

Once the HTTP Client has communicated the JID and transaction identifier to the HTTP Server, the HTTP Server MUST verify that the JID is authorized to access the HTTP resource. This may involve JID-level or domain-level access checks, or (depending on local service policies) potentially no access checks at all if only verification is required.

If the JID is authorized to access the HTTP resource, the HTTP Server MUST pass the JID and transaction identifier to the XMPP Server for confirmation. Exactly how this is done is up to the implementation. The most likely scenario is for the HTTP Server to connect to the XMPP Server as a trusted server component, although it would also be possible for the XMPP Server to provide an HTTP interface.

4.5 XMPP Server Requests Confirmation via XMPP

Upon receiving the JID and transaction identifier from the HTTP Server, the XMPP Server MUST send a confirmation request (via XMPP) to the XMPP Client.

The confirmation request shall consist of an empty <confirm/> element qualified by the ''http://jabber.org/protocol/http-auth' namespace. This element MUST possess a 'method' attribute whose value is the method of the HTTP request, MUST possess a 'url' attribute whose value is the full HTTP URL that was requested, and MUST possess an 'id' attribute whose value is the transaction identifier provided in the HTTP Authorization Request.

If the JID provided was a full JID, the confirmation request SHOULD be sent in an <iq/> stanza of type "get" whose 'to' attribute is set to the full JID, but MAY be sent in a <message/> stanza.

If the JID provided was a bare JID, the confirmation request MUST be sent in a <message/> stanza whose 'to' attribute is set to the bare JID; this enables delivery to the "most available" resource for the user (however "most available" is determined by the XMPP Server). The <message/> stanza MAY include a <body/> element that provides human-readable information or instructions.

Example 5. Confirmation Request Sent via IQ

<iq type='get' 
    from='files.shakespeare.lit' 
    to='juliet@capulet.com/balcony' 
    id='ha000'>
  <confirm xmlns='http://jabber.org/protocol/http-auth'
           id='transaction-identifier'
           method='GET'
           url='https://files.shakespeare.lit:9345/missive.html'/>
</iq>
    

Example 6. Confirmation Request Sent via Message

<message type='normal'
         from='files.shakespeare.lit' 
         to='juliet@capulet.com'>
  <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  <body>
    Someone (maybe you) has requested the file 
    https://files.shakespeare.lit:9345/missive.html.
    If you wish to confirm the request, please reply
    to this message by typing "OK". If not, please 
    reply with "No".
  </body>
  <confirm xmlns='http://jabber.org/protocol/http-auth'
           id='transaction-identifier'
           method='GET'
           url='https://files.shakespeare.lit:9345/missive.html'/>
</message>
    

4.6 XMPP Client Confirms Request via XMPP

If the confirmation request was provided via an <iq/> stanza, the XMPP Client MUST respond to the request by sending an <iq/> stanza back to the XMPP Server. If the user wishes to confirm the request, the <iq/> response stanza MUST be of type "result" and MAY contain the original <confirm/> child element (although this is not necessary since the XMPP 'id' attribute can be used for tracking purposes):

Example 7. XMPP Client Confirms Request via IQ

<iq type='result' 
    from='juliet@capulet.com/balcony' 
    to='files.shakespeare.lit' 
    id='ha000'/>
    

If the user wishes to deny the request, the <iq/> response stanza MUST be of type "error", MAY contain the original <confirm/> child element (although this is not necessary since the XMPP 'id' attribute can be used for tracking purposes), and MUST specify an error, which SHOULD be <not-authorized/>:

Example 8. XMPP Client Denies Request via IQ

<iq type='error' 
    from='juliet@capulet.com/balcony' 
    to='files.shakespeare.lit' 
    id='ha000'>
  <confirm xmlns='http://jabber.org/protocol/http-auth'
           id='transaction-identifier'
           method='GET'
           url='https://files.shakespeare.lit:9345/missive.html'/>
  <error code='401' type='auth'>
    <not-authorized xmlns='urn:ietf:params:xml:xmpp-stanzas'/>
  </error>
</iq>
    

If the confirmation request was provided via a <message/> stanza and the <message/> contains a human-readable <body/> or does not contain a <body/> but the XMPP Client understands the 'http://jabber.org/protocol/http-auth' namespace, the XMPP Client SHOULD respond to the request by sending a <message/> stanza back to the XMPP Server. If the user wishes to confirm the request, the <message/> response stanza SHOULD be of type "normal", MUST mirror the <thread/> ID (if provided by the XMPP Server), and MAY contain the original <confirm/> child element (although this is not required):

Example 9. XMPP Client Confirms Request via Message

<message from='juliet@capulet.com/balcony'
         to='files.shakespeare.lit'>
  <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  <confirm xmlns='http://jabber.org/protocol/http-auth'
           id='transaction-identifier'
           method='GET'
           url='https://files.shakespeare.lit:9345/missive.html'/>
</message>
    

If the user wishes to deny the request, the <message/> response stanza MUST be of type "error", MUST mirror the <thread/> ID (if provided by the XMPP Server), MAY (but is not required to) contain the original <confirm/> child element, and MUST specify an error, which SHOULD be <not-authorized/>:

Example 10. XMPP Client Denies Request via Message

<message type='error' 
         from='juliet@capulet.com/balcony'
         to='files.shakespeare.lit'>
  <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  <confirm xmlns='http://jabber.org/protocol/http-auth'
           id='transaction-identifier'
           method='GET'
           url='https://files.shakespeare.lit:9345/missive.html'/>
  <error code='401' type='auth'>
    <not-authorized xmlns='urn:ietf:params:xml:xmpp-stanzas'/>
  </error>
</message>
    

4.7 HTTP Server Allows HTTP Client to Access Object

Once the XMPP Client has successfully confirmed the request, the XMPP Server forwards that confirmation to the HTTP Server, which allows access:

Example 11. HTTP Server Allows Access to Object

200 OK HTTP/1.1
Content-Type: text/html
Content-Length: 3032

...
    

If the XMPP Client denied the request, the HTTP Server MUST return a Forbidden error:

Example 12. HTTP Server Denies Access to Object

403 Forbidden HTTP/1.1
    

5. Implementation Notes

5.1 Interaction of HTTP methods

For the HEAD and OPTIONS methods, the credentials SHOULD be usable for a subsequent request from the same entity. This enables an entity to both determine support for the mechanism defined herein and start the authentication process.

For the POST and PUT methods (or any method containing a message body), clients MUST send all data with each request; the HTTP server is under no obligation to assume that the client will fail. This is especially true since the client can obtain credentials with a previous HEAD or OPTIONS method.

6. Security Considerations

6.1 Association of Request

In order to associate the HTTP request with the XMPP confirmation, a transaction identifier MUST be provided by the user in the HTTP Authorization Request, then passed unchanged to the XMPP Client as the value of the <confirm/> element's 'id' attribute. If the XMPP Client generated the HTTP request, it MUST check the transaction identifier against the requests it has made to verify that the request has not yet been confirmed. If the XMPP Client did not generate the HTTP request, it MUST present the transaction identifier to the user for confirmation. If the XMPP Client or User confirms the request, the XMPP Client MUST then return a confirmation to the XMPP Server for delivery to the HTTP Server.

6.2 Strength of Authentication Schemes

Section 4.6 of RFC 2617 specifies that if an HTTP server returns multiple challenges with a 401 (Authenticate) response, an HTTP client must use the strongest authentication scheme it understands. For the purposes of this document, an HTTP client MUST consider the HTTP Digest scheme to be stronger than the HTTP Basic scheme.

6.3 Channel Encryption

To reduce the likelihood of man-in-the-middle attacks, channel encryption SHOULD be used for both the XMPP channel and the HTTP channel. In particular:

  1. The channel used for HTTP requests and responses SHOULD be encrypted via SSL (secure HTTP via https: URIs) or TLS (RFC 2817 [7]).
  2. If the standard binding of XMPP to TCP is used, TLS SHOULD be negotiated for the XMPP channel in accordance with RFC 3920.
  3. If a binding of XMPP to HTTP is used (e.g., as specified in JEP-0124), exchanges between the XMPP Client and XMPP Server (connection manager) SHOULD be sent over a channel that is encrypted using SSL or TLS.

6.4 End-to-End Encryption

For added security, the XMPP Server and XMPP Client may wish to communicate using end-to-end encryption. Methods for doing so are outside the scope of this proposal.

7. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [8].

8. Jabber Registrar Considerations

8.1 Protocol Namespaces

The Jabber Registrar [9] shall include "http://jabber.org/protocol/http-auth" in its registry of protocol namespaces.

9. XML Schema

<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://jabber.org/protocol/http-auth'
    xmlns='http://jabber.org/protocol/http-auth'
    elementFormDefault='qualified'>
  
  <xs:element name='confirm'>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='empty'>
          <xs:attribute name='id' use='required' type='xs:string'/>
          <xs:attribute name='method' use='required' type='xs:NCName'/>
          <xs:attribute name='url' use='required' type='xs:anyURI'/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>
  
  <xs:simpleType name='empty'>
    <xs:restriction base='xs:string'>
      <xs:enumeration value=''/>
    </xs:restriction>
  </xs:simpleType>

</xs:schema>
  


Notes

1. RFC 2616: Hypertext Transport Protocol -- HTTP/1.1 <http://www.ietf.org/rfc/rfc2616.txt>.

2. RFC 2617: HTTP Authentication: Basic and Digest Access Authentication <http://www.ietf.org/rfc/rfc2617.txt>.

3. RFC 3920: Extensible Messaging and Presence Protocol (XMPP): Core <http://www.ietf.org/rfc/rfc3920.txt>.

4. JEP-0066: Out of Band Data <http://www.jabber.org/jeps/jep-0066.html>.

5. RFC 3548: The Base16, Base32, and Base64 Data Encodings <http://www.ietf.org/rfc/rfc3548.txt>.

6. RFC 3986: Uniform Resource Identifiers (URI): Generic Syntax <http://www.ietf.org/rfc/rfc3986.txt>.

7. RFC 2817: Upgrading to TLS Within HTTP/1.1 <http://www.ietf.org/rfc/rfc2817.txt>.

8. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

9. The Jabber Registrar maintains a list of reserved Jabber protocol namespaces as well as registries of parameters used in the context of protocols approved by the Jabber Software Foundation. For further information, see <http://www.jabber.org/registrar/>.


Revision History

Version 0.9 (2005-11-09)

Changed use of transaction identifier from SHOULD to MUST; removed x-xmpp-auth scheme; clarified requirements, business rules, and confirm element syntax; added several more examples; more clearly specified how HTTP server communicates with XMPP server; updated schema and security considerations. (psa)

Version 0.8 (2005-10-19)

Changed use of transaction identifier from MAY to SHOULD; updated and clarified security considerations. (psa)

Version 0.7 (2005-10-11)

Added more HTTP examples to illustrate process flow; updated IANA considerations and security considerations. (psa)

Version 0.6 (2005-07-21)

Updated references; clarified several points in the text; rewrote introduction. (psa)

Version 0.5 (2004-04-27)

Added optional id attribute in order to track requests, described in new implementation note. (psa)

Version 0.4 (2004-01-14)

Incorporated results of IRL and IM discussions: simplified the flow; added x-xmpp-auth authentication scheme. (psa/dss/jh)

Version 0.3 (2003-06-27)

Removed hashing requirements; added/clarified JID fields in HTTP headers; added XML Schema; added XMPP error conditions; added more descriptions for confirm and accept tokens; fixed discrepancies in examples. (lw)

Version 0.2 (2003-06-26)

Updated to reflect feedback received (moved to using standard HTTP authentication headers; included token-authority JID in HTTP header; removed example involving deprecated JEP). (lw)

Version 0.1 (2003-01-31)

Initial draft. (lw)


END