XEP-0389: Extensible In-Band Registration

Abstract: This specification defines an XMPP protocol extension for in-band registration with instant messaging servers and other services with which an XMPP entity may initiate a stream. It aims to improve upon the state of the art and replace XEP-0077: In-Band Registration by allowing multi-factor registration mechanisms, and account recovery.
Author:Sam Whited
Copyright:© 1999 – 2017 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status:Experimental
Type:Standards Track
Version:0.1.0
Last Updated:2017-03-16

WARNING: This Standards-Track document is Experimental. Publication as an XMPP Extension Protocol does not imply approval of this proposal by the XMPP Standards Foundation. Implementation of the protocol described herein is encouraged in exploratory implementations, but production systems are advised to carefully consider whether it is appropriate to deploy implementations of this protocol before it advances to a status of Draft.


Table of Contents


1. Introduction
2. Requirements
3. Glossary
4. Use Cases
5. Discovering Support
6. Challenges
7. Completing Registration or Recovery
8. Internationalization Considerations
9. Security Considerations
10. IANA Considerations
11. XMPP Registrar Considerations
    11.1. Protocol Namespaces
    11.2. IBR Challenge Types Registry
    11.3. Challenge Types
    11.4. Namespace Versioning

Appendices
    A: Document Information
    B: Author Information
    C: Legal Notices
    D: Relation to XMPP
    E: Discussion Venue
    F: Requirements Conformance
    G: Notes
    H: Revision History


1. Introduction

Historically, registering with an XMPP service has been difficult. Each server either used customized out-of-band registration mechanisms such as web forms which were difficult to discover, or they used In-Band Registration (XEP-0077) [1] which could easily be abused by spammers to register large numbers of accounts and which allowed for only limited extensibility.

To solve these issues this specification provides a new in-band registration protocol that allows servers to present the user with a series of "challenges". This allows for both multi-stage proof-of-posession registration flows and spam prevention mechanisms such as proof-of-work functions.

2. Requirements

3. Glossary

Proof-of-work (PoW)
A proof-of-work protocol requires that a client perform a computationally intense task which is easily verified by the server.
Proof-of-possession (PoP)
A proof-of-possession protocol requires that a client prove that they have posession of some resource (eg. a shared secret, or a valid mobile phone number).

4. Use Cases

5. Discovering Support

If a server supports registering for or recovering an account using Extensible IBR, it MUST inform the connecting client when returning stream features during the stream negotiation process. This is done by including a <register/> element, qualified by the 'urn:xmpp:register:0' namespace for account registration, or a <recovery/> element qualified by the same namespace for account recovery. The register and recovery features are always voluntary-to-negotiate. The registration and recovery features MUST NOT be advertised before encryption has been negotiated, eg. using direct-TLS or STARTTLS. They SHOULD be advertised at the same time as the SASL authentication feature, meaning that after registration or recovery is completed SASL authentication can proceed.

For recovery or registration, the server MUST include a list of all challenge types which the client may receive during the course of registering or recovering an account. The purpose of this list is to allow clients to detect if registration requires a challenge type which the client does not support, so servers SHOULD only include each type once; the list is merely informative, and should not be relied upon by clients except to ensure that all mechanisms are supported. This list should comprise <challenge/> elements containing a string that uniquely identifies the type of challenge being issued.

Example 1. Host Advertises Stream Features

<stream:features>
  <mechanisms xmlns='urn:xmpp:sasl:0'>
    <mechanism>EXTERNAL</mechanism>
    <mechanism>SCRAM-SHA-1-PLUS</mechanism>
    <mechanism>SCRAM-SHA-1</mechanism>
    <mechanism>PLAIN</mechanism>
  </mechanisms>
  <register xmlns='urn:xmpp:register:0'>
    <challenge>jabber:x:data'</challenge>
    <challenge>pow-example</challenge>
  </register>
  <recovery xmlns='urn:xmpp:register:0'>
    <challenge>jabber:x:oob</challenge>
  </recovery>
</stream:features>

6. Challenges

A client selects the registration or recovery feature for negotiation by replying with an empty element of the same name and namespace. For example, to attempt account recovery the client would send a <recovery> element qualified by the 'urn:xmpp:register:0' namespace.

The server then replies with a challenge. Challenges take the form of a <challenge/> element qualified by the 'urn:xmpp:register:0' namespace with a 'type' attribute containing the challenge type and containing a challenge data payload.

Type type of a challenge is a value which identifes what sort of payload a client might expect. This document defines a type of 'jabber:x:data' which MUST always contain a data form (an 'x' element with type 'form') as defined by Data Forms (XEP-0004) [2]. Other types may be defined in the future. For example, a challenge containing a data form might look like the following:

Example 2. Host Returns Registration Form to Entity

<challenge xmlns='urn:xmpp:register:0'
           type='jabber:x:data'>
  <x xmlns='jabber:x:data' type='form'>
    <title>Chat Registration</title>
    <instructions>
      Please provide the following information
      to sign up to view our chat rooms!
    </instructions>
    <field type='hidden' var='FORM_TYPE'>
      <value>urn:xmpp:register:0</value>
    </field>
    <field type='text-single' label='Given Name' var='first'/>
    <field type='text-single' label='Family Name' var='last'/>
    <field type='text-single' label='Nickname' var='nick'>
      <required/>
    </field>
    <field type='text-single' label='Recovery Email Address' var='email'>
      <required/>
    </field>
  </x>
</challenge>

After a challenge is received, the client replies to the challenge by sending a <response/> element qualified by the 'urn:xmpp:register:0' namespace or a cancelation as defined later in this document. If the client sends a response, it MUST also include a payload defined by the specific challenge type. In the case of a jabber:x:data challenge, the payload should be a form submission as defined by Data Forms (XEP-0004) [2] (an 'x' element of type 'submit'). For instance, to reply to the data form challenge from the previous example a client might send:

Example 3. User Submits Registration Form

<response xmlns='urn:xmpp:register:0'>
  <x xmlns='jabber:x:data' type='submit'>
    <field type='hidden' var='FORM_TYPE'>
      <value>urn:xmpp:register:0</value>
    </field>
    <field type='text-single' label='Given Name' var='first'>
      <value>Juliet</value>
    </field>
    <field type='text-single' label='Family Name' var='last'>
      <value>Capulet</value>
    </field>
    <field type='text-single' label='Nickname' var='nick'>
      <value>Jule</value>
    </field>
    <field type='text-single' label='Recovery Email Address' var='email'>
      <value>juliet@capulet.com</value>
    </field>
  </x>
</response>

If after receiving a challenge a client does not wish to continue registration or recovery, it may send an empty <cancel> element qualified by the 'urn:xmpp:register:0' namespace. This informs the server that registration is complete. This is the same as submitting a data form of type 'cancel' in response to a data form challenge.

Example 4. User Cancels Registration or Recovery

<cancel xmlns='urn:xmpp:register:0'/>

7. Completing Registration or Recovery

If the client submits invalid data, or the server wishes to cancel for some other reason, it may reply with an empty <cancel/> element qualified by the 'urn:xmpp:register:0' namespace. If the client successfully completes the challenge, the server MAY return an empty <success/> element qualified by the 'urn:xmpp:register:0' namespace, at which point it may continue with the stream negotiation process. If the server needs more information, for example, in the previous challenge the user entered an email and now the server wishes to ask for a code that was sent to that email, the server MAY send another challenge.

8. Internationalization Considerations

When providing instructions in a data form the server SHOULD use the language specified in the XML stream's current xml:lang, or the closest language for which the server has a translation (eg. based on mutual intelligibility between scripts and languages).

For more information about language tags and matching, see BCP 47 [3]

9. Security Considerations

Servers that allow in-band registration need to take measures to prevent abuse. Common techniques to prevent spam registrations include displaying CAPTCHAs or requiring proof-of-posession of a valid email address or telephone number by sending a unique code (e.g. an HMAC that can later be verified as having originated at the server) to the users email and requiring that they enter the code before continuing. Servers that do not take such measures risk being black listed by other servers in the network.

10. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [4].

11. XMPP Registrar Considerations

11.1 Protocol Namespaces

This specification defines the following XML namespace:

Upon advancement of this specification from a status of Experimental to a status of Draft, the XMPP Registrar [5] shall add the foregoing namespace to the registry located at <https://xmpp.org/registrar/stream-features.html>, as described in Section 4 of XMPP Registrar Function (XEP-0053) [6].

11.2 IBR Challenge Types Registry

The XMPP Registrar shall maintain a registry of IBR challenge types. Challenge types defined within the XEP series MUST be registered with the XMPP Registrar.

In order to submit new values to this registry, the registrant shall define an XML fragment of the following form and either include it in the relevant XMPP Extension Protocol or send it to the email address <registrar@xmpp.org>:

<challenge>
  <name>The name of the challenge type.</name>
  <desc>A natural-language summary of the challenge.</desc>
  <payloaddoc>
    The document in which the IBR challenge payload is specified.
  </payloaddoc>
  <doc>
    The doucment in which the IBR challenge itself is specified (may be the same
    as <payloaddoc/>).
  </doc>
</challenge>

For an example registration, see the next section.

11.3 Challenge Types

This specification defines the following IBR challenge types:

Upon advancement of this specification from a status of Experimental to a status of Draft, the XMPP Registrar [5] shall add the following definition to the IBR challenge types registry, as described in this document:

<challenge>
  <name>Data Forms Challenge</name>
  <desc>Requests that the client fill out an XEP-0004 data form.</desc>
  <payloaddoc>XEP-0004</payloaddoc>
  <doc>TODO: Insert this document once it is assigned a number</doc>
</profile>

11.4 Namespace Versioning

If the protocol defined in this specification undergoes a revision that is not fully backwards-compatible with an older version, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.


Appendices


Appendix A: Document Information

Series: XEP
Number: 0389
Publisher: XMPP Standards Foundation
Status: Experimental
Type: Standards Track
Version: 0.1.0
Last Updated: 2017-03-16
Approving Body: XMPP Council
Dependencies: XMPP Core
Supersedes: XEP-0077
Superseded By: None
Short Name: ibr2
Source Control: HTML
This document in other formats: XML  PDF


Appendix B: Author Information

Sam Whited

Email: sam@samwhited.com
JabberID: sam@samwhited.com
URI: https://blog.samwhited.com/


Appendix C: Legal Notices

Copyright

This XMPP Extension Protocol is copyright © 1999 – 2017 by the XMPP Standards Foundation (XSF).

Permissions

Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).

Appendix D: Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards 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 document 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.


Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.

Errata can be sent to <editor@xmpp.org>.


Appendix F: Requirements Conformance

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


Appendix G: Notes

1. XEP-0077: In-Band Registration <https://xmpp.org/extensions/xep-0077.html>.

2. XEP-0004: Data Forms <https://xmpp.org/extensions/xep-0004.html>.

3. BCP 47: Tags for Identifying Languages <http://tools.ietf.org/html/bcp47>.

4. 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/>.

5. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.

6. XEP-0053: XMPP Registrar Function <https://xmpp.org/extensions/xep-0053.html>.


Appendix H: Revision History

Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/

Version 0.1.0 (2017-03-16)

(XEP Editor (ssw))

Version 0.0.2 (2017-02-15)

(ssw)

Version 0.0.1 (2017-02-08)

First draft.

(ssw)

END