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Aggregated Service Discovery
draft-daboo-aggregated-service-discovery-01

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Andrew McMillan, Cyrus Daboo
Last updated 2012-10-15
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draft-daboo-aggregated-service-discovery-01
Network Working Group                                        A. McMillan
Internet-Draft                                                  Morphoss
Intended status: Standards Track                                C. Daboo
Expires: April 18, 2013                                       Apple Inc.
                                                        October 15, 2012

                      Aggregated Service Discovery
              draft-daboo-aggregated-service-discovery-01

Abstract

   This specification describes how clients can discover multiple
   services to configure themselves with a minimum of user-provided
   information, as short as possible sequence of queries and with a
   minimum of overhead for administrators of the services.

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 April 18, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Conventions Used in This Document  . . . . . . . . . . . . . .  4
   4.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   5.  Aggregated Service Discovery Document Format . . . . . . . . .  5
     5.1.  SD:servicediscovery  . . . . . . . . . . . . . . . . . . .  5
       5.1.1.  SD:provider  . . . . . . . . . . . . . . . . . . . . .  5
         5.1.1.1.  SD:name  . . . . . . . . . . . . . . . . . . . . .  5
         5.1.1.2.  SD:description . . . . . . . . . . . . . . . . . .  5
         5.1.1.3.  SD:image . . . . . . . . . . . . . . . . . . . . .  5
         5.1.1.4.  SD:contact . . . . . . . . . . . . . . . . . . . .  5
         5.1.1.5.  SD:manage  . . . . . . . . . . . . . . . . . . . .  6
       5.1.2.  SD:entry . . . . . . . . . . . . . . . . . . . . . . .  6
         5.1.2.1.  SD:service . . . . . . . . . . . . . . . . . . . .  6
         5.1.2.2.  SD:application . . . . . . . . . . . . . . . . . .  6
         5.1.2.3.  SD:priority  . . . . . . . . . . . . . . . . . . .  6
         5.1.2.4.  SD:host  . . . . . . . . . . . . . . . . . . . . .  6
         5.1.2.5.  SD:port  . . . . . . . . . . . . . . . . . . . . .  7
         5.1.2.6.  SD:tls . . . . . . . . . . . . . . . . . . . . . .  7
         5.1.2.7.  SD:auth  . . . . . . . . . . . . . . . . . . . . .  7
   6.  Finding the Aggregated Service Discovery Information . . . . .  7
   7.  Handling multiple, alternative services  . . . . . . . . . . .  7
   8.  Internationalization Considerations  . . . . . . . . . . . . .  8
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
     10.1. Namespace Registration . . . . . . . . . . . . . . . . . .  9
     10.2. Media Type . . . . . . . . . . . . . . . . . . . . . . . .  9
     10.3. Well-Known URI Registration  . . . . . . . . . . . . . . . 10
       10.3.1. servicediscovery Well-Known URI Registration . . . . . 10
   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 10
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     12.2. Informative References . . . . . . . . . . . . . . . . . . 11
   Appendix A.  Change History (to be removed prior to
                publication as an RFC)  . . . . . . . . . . . . . . . 11
   Appendix B.  Aggregated Service Discovery Schema . . . . . . . . . 11
   Appendix C.  Example of multiple services  . . . . . . . . . . . . 13
   Appendix D.  Example - multiple, alternative mail retrieval
                services  . . . . . . . . . . . . . . . . . . . . . . 15

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1.  Introduction

   There are currently various systems in place for discovery and
   configuration of individual protocols, but the process can often
   require an extensive series of requests using different protocols to
   discover all of the details needed to set up the various client
   services which an individual might use to interact with an
   organisation or service provider.

   Consider Jason, a new employee at Example Enterprises.  Jason needs
   to configure his e-mail program to use IMAP [RFC3501] + TLS on port
   143 against mail.example.com, he needs to send mail on port 8557 via
   TLS+SMTP to smtp.example.com, his calendar is on port 8443 at
   https://caldav.example.com:8443/calendar/, and so forth.  Some of
   these things can be discovered relatively easily, with a combination
   of DNS queries (including SRV lookups, certificate checking, and http
   requests).  However, each protocol has its own requirements and
   settings and each has to be done separately.  Whilst the client can
   "hide" the multiple service setup from the user, the actual
   implementation often requires separate code and processes to manage,
   making it more complex that it needs to be.

   This specification defines a single protocol which will allows for
   discovery of a variety of services in a single call, allowing
   developers to simplify the coding and user interface in client
   software, and in particular in multi-function client software such as
   a combined e-mail and calendar client.

2.  Open Issues

   1.  XML vs JSON for the document format

   2.  Support custom service attributes without the need for formal
       registration?  If so, would we need a "critical" attribute to
       indicate ones that must be understood?

   3.  Is it OK to embed certificate details for the actual services or
       a root certificate?

   4.  Do we want to support delegation of service information to
       another service discovery document?  That might be useful in
       cases where different services at the same domain are under the
       control of different "authorities".

   5.  Should we define a local area network discovery mechanism? i.e.,
       client connects to local network and immediately sees a set of
       services it could configure for the user.

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   6.  Should we specify whether clients should re-check account
       information on a regular basis for updates, or should we rely on
       in-protocol account redirection?

3.  Conventions Used in This Document

   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].

   The namespace "urn:ietf:params:xml:ns:servicediscovery" is reserved
   for the XML elements defined in this specification.  XML elements
   defined by individual implementations MUST NOT use the
   "urn:ietf:params:xml:ns:caldav" namespace, and instead should use a
   namespace that they control.

4.  Overview

   The following outlines the steps a client carries out to setup
   multiple services for a user:

   1.  The client software is expected to capture a user identifier and
       domain name (possibly entered in the form of an email address)
       from the user, and possibly a password. e.g.,
       'cyrus@example.com'.

   2.  The client would make an initial DNS SRV [RFC2782] query for
       '_servicediscovery._tcp.example.com'.  The result of the SRV
       lookup will be a hostname that is then used in place of the user
       supplied domain name for the next steps.  If the SRV lookup is
       unsuccessful, then the user supplied domain name is used for the
       next steps.

   3.  The client then makes an HTTP GET request [RFC2616] against the
       server, using TLS [RFC2818], requesting the URL 'https://{domain
       name}/.well-known/servicediscovery?id={user identifier}', where
       '{domain name}' is the host name determined from step #2, and
       '{user identifier}' is the user supplied identifier from step #1.
       The client will follow any redirects and respond to any
       authentication challenges.  Where the user did not provide an
       appropriate authentication token in the first step the client
       software will prompt for it at this point

   4.  The client will receive an XML document in step #3 conforming to
       the format described in Section 5.  The client parses this
       document to extract information about the available services.  At
       that point it can either present a list of services to the user
       so that they can decide exactly what they want setup, or it can

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       automatically setup services for all those it supports.

5.  Aggregated Service Discovery Document Format

   The aggregated service discovery document is an XML document.  The
   document contains two groups of information: overall service provider
   information (e.g., name, icon "badge", contact information), and a
   list of each service supported.  Each service will contain some
   information common to each type of service, and then information
   specific to each service.

   The XML DTD is defined in Appendix B.  Each element is described
   below.  An example of such an aggregated service discovery document
   for some common services is shown in Appendix C.

5.1.  SD:servicediscovery

   The root element for the document

5.1.1.  SD:provider

   Contains information describing the service provider, that can be
   used by clients to "group" individual services together under a
   common name or section when presenting details to the user.

5.1.1.1.  SD:name

   The name for the service provider.

5.1.1.2.  SD:description

   The description of the service provider.

5.1.1.3.  SD:image

   An image that can be used as an "icon" for the service provider.  The
   image data MUST be base64 encoded.  The image SHOULD NOT exceed a
   size of 128 x 128 pixels.

5.1.1.4.  SD:contact

   Contact information for the service provider.

5.1.1.4.1.  SD:email

   An email address that can be used to contact the service provider.

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5.1.1.4.2.  SD:uri

   A URI for a webpage providing information about the service provider.

5.1.1.5.  SD:manage

   A URI for a webpage where a user can manage details of their account.
   e.g., a place where users can go to add additional (possibly payment
   required) services.

5.1.2.  SD:entry

   Provides detail for a specific service

5.1.2.1.  SD:service

   The service type.  This MUST be an IANA registered service type.  The
   service type will determine what additional information is present
   within the enclosing SD:entry element.

5.1.2.2.  SD:application

   Identifies the nature of the service to allow similar services to be
   grouped together.  This is used in conjunction with the SD:priority
   element to group services of different types so that only one of the
   services within the group will be configured.  For example, the IMAP
   [RFC3501] and POP3 [RFC1939] protocols will have SD:service values of
   'imap' and 'pop3' respectively, and they could be given the same SD:
   application value of 'mailstore'.  If the service provider prefers
   its users to use IMAP over POP3 (assuming the client supports IMAP),
   then the SD:priority value for the IMAP service would have a higher
   value than that for the POP3 service.

5.1.2.3.  SD:priority

   A positive, non-zero integer value that is used by the service
   provider to indicate a preference for one particular service over
   another within the same application group.  Multiple services within
   a group may share the same priority, indicating that the service
   provider does not wish to express a preference.  Services with a
   higher numbered priority are to be preferred over lower numbered
   ones.

5.1.2.4.  SD:host

   The hostname of the server providing the service.

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5.1.2.5.  SD:port

   The network port number of the server providing the service.

5.1.2.6.  SD:tls

   Provides detail of transport layer security to be used with the
   service.

5.1.2.6.1.  SD:required

   If present, indicates that clients MUST use transport layer security
   when connecting to the server providing the service.

5.1.2.6.2.  SD:certificate

   TODO: not sure we should have this as opposed to relying on normal
   certificate verification for each service.  If present, indicates
   details about TLS certificates that the server will present to the
   client during TLS negotiation.  Clients can use these certificate
   details to "short circuit" certificate verification for the service.

5.1.2.7.  SD:auth

   Provides detail of authentication to be used with the service.

   TODO element details

6.  Finding the Aggregated Service Discovery Information

   A ".well-known" URI is registered by this specification:
   "servicediscovery" (see Section 10).  This URI points to a resource
   that the client can use to retrieve the aggregated service discovery
   document for the site.  Clients MUST handle HTTP redirects on the
   ".well-known" URI.  Clients MUST handle HTTP authentication on the
   ".well-known" URI.

   When requesting the document clients MUST include a URI query
   parameter "id" set to the user identifier entered by the user.  When
   responding to the request, the server MUST tailor the aggregated
   service discovery document for the user making the request and MUST
   require HTTP authentication by that user before returning the
   document.

7.  Handling multiple, alternative services

   The SD:application and SD:priority elements provide a way for a
   service provider to distinguish multiple services of the same type,

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   as well as allow the client to select the most appropriate service
   when several alternatives exist.

   For example, consider the case of a service provider supporting two
   separate email retrieval services, one the "primary" account, and the
   other for "internal" messaging only.  It is expected that clients
   configure accounts for both services.  Each service also offers
   either IMAP [RFC3501] or POP3 [RFC1939] as an email retrieval
   protocol.  In this case the aggregated service discovery document
   would contain four SD:entry elements: two describing an IMAP service
   and two describing a POP3 service.  Each entry would contain an SD:
   application element that groups one IMAP and one POP3 service
   together for each of the "primary" and "internal" account groups.
   Each entry would also contain an SD:priority element indicating the
   service providers preference for clients to use either IMAP or POP3.
   An example of such an aggregated service discovery document is shown
   in Appendix D.

   When a client retrieves and processes such a document, it would first
   group services based on the SD:application value.  For each group, it
   iterates over the list of entries in the group, ordered by SD:
   priority values, and configures an account for the first one it finds
   with an SD:service that it supports.

8.  Internationalization Considerations

   Some elements of the service discovery document can contain human
   readable text that clients might choose to present to a user.
   Clients SHOULD use the Accept-Language header behavior described in
   Section 14.4 of [RFC2616] to ensure the server can return a document
   suitable for the user's chosen language.  Servers SHOULD support
   variations of the service discovery document based on language,
   returning the appropriate variation in response to client requests.
   When doing so the xml:lang attribute SHOULD be included on all XML
   elements in the document that have been localized.

9.  Security Considerations

   When using an SRV lookup to discover a server hosting the service
   discovery document, a malicious attacker with access to the DNS
   server data, or able to get spoofed answers cached in a recursive
   resolver, can potentially cause clients to connect to a server
   hosting a bogus service discovery document with service data chosen
   by the attacker.  In the absence of a secure DNS option, clients
   SHOULD check that the target FQDN returned in the SRV record matches
   the original service domain that was queried.  If the target FQDN is
   not in the queried domain, clients SHOULD verify with the user that
   the SRV target FQDN is suitable for use before executing any

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   connections to the host.

   HTTP requests for the service-discovery document MUST be performed
   via TLS.  Clients MUST use the procedure outlined in Section 4.3 of
   [RFC6125] to verify the service.

10.  IANA Considerations

10.1.  Namespace Registration

   Registration request for the aggregated service discovery namespace:

      URI: urn:ietf:params:xml:ns:servicediscovery

      Registrant Contact: IESG

      XML: None.  Namespace URIs do not represent an XML specification.

10.2.  Media Type

   This section defines the MIME media type for use with the aggregated
   service discovery XML data.

   Type name:  application

   Subtype name:  servicediscovery+xml

   Required parameters:  none

   Optional parameters:  charset as defined for application/xml in
      [RFC3023]; per [RFC3023], use of the charset property parameter
      with the value "utf-8" is "STRONGLY RECOMMENDED"

   Encoding considerations:  Same as encoding considerations of
      application/xml as specified in [RFC3023]

   Security considerations:  See Section 9.

   Interoperability considerations:  This media type provides a format
      for aggregated service discovery information based on XML.

   Published specification:  This specification.

   Applications which use this media type:  Applications that configure
      services.

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   Additional information:

      Magic number(s):  None

      File extension(s):  None

      Macintosh file type code(s):  None specified.

   Person & email address to contact for further information:  IESG

   Intended usage:  COMMON

   Restrictions on usage:  There are no restrictions on where this media
      type can be used.

   Author:  See the "Author's Address" section of this document.

   Change controller:  IETF

10.3.  Well-Known URI Registration

   This document defines a ".well-known" URI using the registration
   procedure and template from Section 5.1 of [RFC5785].

10.3.1.  servicediscovery Well-Known URI Registration

   URI suffix:  servicediscovery

   Change controller:  IETF.

   Specification document(s):  This RFC.

   Related information:  None.

11.  Acknowledgments

12.  References

12.1.  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.

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for

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              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC3023]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media
              Types", RFC 3023, January 2001.

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              April 2010.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, March 2011.

12.2.  Informative References

   [RFC1939]  Myers, J. and M. Rose, "Post Office Protocol - Version 3",
              STD 53, RFC 1939, May 1996.

   [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, March 2003.

Appendix A.  Change History (to be removed prior to publication as an
             RFC)

   Changes in -01:

   1.  Renamed various elements for clarity.

   2.  Added an SD:manage element.

   3.  Added a section on handling of multiple, alternative services,
       together with a second appendix example.

Appendix B.  Aggregated Service Discovery Schema

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   <!ELEMENT servicediscovery (provider?, entry*) >

     <!ELEMENT provider (name?, description?, image?,
                         contact?, manage?) >

       <!ELEMENT name (#PCDATA) >

       <!ELEMENT description (#PCDATA) >

       <!ELEMENT image (#PCDATA) >

       <!ELEMENT contact (email?, uri?) >

         <!ELEMENT email (#PCDATA) >
         <!ELEMENT uri (#PCDATA) >

       <!ELEMENT manage (#PCDATA) >

     <!ELEMENT entry (service, (application, priority)?,
                         host?, port?, tls?, auth?, ANY) >

       <!ELEMENT service (#PCDATA) >

       <!ELEMENT application (#PCDATA) >

       <!ELEMENT priority (#PCDATA) >

       <!ELEMENT host (#PCDATA) >

       <!ELEMENT port (#PCDATA) >

       <!ELEMENT tls (required?, certificate*) >
         <!ELEMENT required EMPTY >
         <!ELEMENT certificate (data|id|hash) >
           <!ELEMENT data (#PCDATA) >
           <!ELEMENT id (#PCDATA) >
           <!ELEMENT hash (#PCDATA) >

       <!ELEMENT auth (type, details?) >
           <!ELEMENT type (#PCDATA) >
           <!ELEMENT details (userpswd|ANY) >
             <!ELEMENT userpswd (userid?, password?) >
               <!ELEMENT userid (#PCDATA) >
               <!ELEMENT password (#PCDATA) >

       <!ELEMENT principal-URL (#PCDATA) >

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Appendix C.  Example of multiple services

   GET /.well-known/servicediscovery?id=cyrus@example.com HTTP/1.1
   Host:example.com:443
   Authorization: basic QmFzZTY0IGlzIGVhc3kgdG8gZGVjb2Rl
   Content-Type: application/servicediscovery+xml
   Content-Length: xxx

   <?xml version="1.0" standalone="no"?>
   <servicediscovery xmlns="urn:ietf:params:xml:ns:servicediscovery">
     <provider>
       <name>Super-duper ISP</name>
       <description>
         Super-duper ISP is the home for all your data.
       </description>
       <contact>
         <email>superduper@example.com</email>
         <uri>http://www.example.com</uri>
       </contact>
       <manage>http://www.example.com/myaccount.html</manage>
     </provider>

     <entry>
       <service>imap</service>
       <application>mail-access</application>
       <priority>2</priority>
       <host>imap.example.com</host>
       <port>143</port>
       <tls>
         <required />
       </tls>
       <auth>
         <type>CRAM-MD5</type>
       </auth>
     </entry>

     <entry>
       <service>pop3</service>
       <application>mail-access</application>
       <priority>1</priority>
       <host>pop.example.com</host>
       <port>110</port>
       <tls>
         <required />
       </tls>
       <auth>
         <type>CRAM-MD5</type>

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       </auth>
     </entry>

     <entry>
       <service>submission</service>
       <host>mail.example.com</host>
       <port>587</port>
       <tls>
         <required />
       </tls>
       <auth>
         <type>CRAM-MD5</type>
       </auth>
     </entry>

     <entry>
       <service>caldav</service>
       <host>calendar.example.com</host>
       <port>443</port>
       <tls>
         <required />
       </tls>
       <auth>
         <type>Digest</type>
       </auth>
       <principal-URL>https://calendar.example.com/principals/
   users/cyrus</principal-URL>
     </entry>

     <entry>
       <service>carddav</service>
       <host>contacts.example.com</host>
       <port>443</port>
       <tls>
         <required />
       </tls>
       <auth>
         <type>Digest</type>
       </auth>
       <principal-URL>https://contacts.example.com/principals/
   users/cyrus</principal-URL>
     </entry>

   </servicediscovery>

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Appendix D.  Example - multiple, alternative mail retrieval services

   GET /.well-known/servicediscovery?id=cyrus@example.com HTTP/1.1
   Host:example.com:443
   Authorization: basic QmFzZTY0IGlzIGVhc3kgdG8gZGVjb2Rl
   Content-Type: application/servicediscovery+xml
   Content-Length: xxx

   <?xml version="1.0" standalone="no"?>
   <servicediscovery xmlns="urn:ietf:params:xml:ns:servicediscovery">
     <provider>
       <name>Mail Agrregator ISP</name>
       <description>
         Primary and internal email services.
       </description>
       <contact>
         <email>emails@example.com</email>
         <uri>http://www.example.com</uri>
       </contact>
       <manage>http://www.example.com/myaccount.html</manage>
     </provider>

     <entry>
       <service>imap</service>
       <application>primary email</application>
       <priority>2</priority>
       <host>imap.example.com</host>
       <port>143</port>
       <tls>
         <required />
       </tls>
       <auth>
         <type>CRAM-MD5</type>
       </auth>
     </entry>

     <entry>
       <service>pop3</service>
       <application>primary email</application>
       <priority>1</priority>
       <host>pop.example.com</host>
       <port>110</port>
       <tls>
         <required />
       </tls>
       <auth>
         <type>CRAM-MD5</type>

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       </auth>
     </entry>

     <entry>
       <service>imap</service>
       <application>internal email</application>
       <priority>2</priority>
       <host>imap.example.com</host>
       <port>143</port>
       <tls>
         <required />
       </tls>
       <auth>
         <type>CRAM-MD5</type>
       </auth>
     </entry>

     <entry>
       <service>pop3</service>
       <application>internal email</application>
       <priority>1</priority>
       <host>pop.example.com</host>
       <port>110</port>
       <tls>
         <required />
       </tls>
       <auth>
         <type>CRAM-MD5</type>
       </auth>
     </entry>

   </servicediscovery>

Authors' Addresses

   Andrew McMillan
   Morphoss Ltd
   6 Karoro Place
   Porirua  5024
   New Zealand

   EMail: andrew@morphoss.com
   URI:   http://www.morphoss.com/

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   Cyrus Daboo
   Apple Inc.
   1 Infinite Loop
   Cupertino, CA  95014
   USA

   EMail: cyrus@daboo.name
   URI:   http://www.apple.com/

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