%ents; BCP 47 BCP 47: Tags for Identifying Languages <http://tools.ietf.org/html/bcp47>." > ]>
Extensible In-Band Registration 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. &LEGALNOTICE; 0389 Experimental Standards Track Standards Council XMPP Core XEP-0077 ibr2 &sam; 0.1.0 2017-03-16 XEP Editor (ssw)
  • Move to experimental.
0.0.2 2017-02-15 ssw
  • Don't allow feature to act as auth.
  • Use a more conventional list for challenge type listings.
0.0.1 2017-02-08 ssw

First draft.

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 &xep0077; 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.

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).

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.

EXTERNAL SCRAM-SHA-1-PLUS SCRAM-SHA-1 PLAIN jabber:x:data' pow-example jabber:x:oob ]]>

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 &xep0004;. Other types may be defined in the future. For example, a challenge containing a data form might look like the following:

Chat Registration Please provide the following information to sign up to view our chat rooms! urn:xmpp:register:0 ]]>

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 &xep0004; (an 'x' element of type 'submit'). For instance, to reply to the data form challenge from the previous example a client might send:

urn:xmpp:register:0 Juliet Capulet Jule juliet@capulet.com ]]>

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.

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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.

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 &bcp47;

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.

This document requires no interaction with &IANA;.

This specification defines the following XML namespace:

  • urn:xmpp:register:0

Upon advancement of this specification from a status of Experimental to a status of Draft, the ®ISTRAR; shall add the foregoing namespace to the registry located at &STREAMFEATURES;, as described in Section 4 of &xep0053;.

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.

®PROCESS; The name of the challenge type. A natural-language summary of the challenge. The document in which the IBR challenge payload is specified. The doucment in which the IBR challenge itself is specified (may be the same as ). ]]>

For an example registration, see the next section.

This specification defines the following IBR challenge types:

  • jabber:x:data

Upon advancement of this specification from a status of Experimental to a status of Draft, the ®ISTRAR; shall add the following definition to the IBR challenge types registry, as described in this document:

Data Forms Challenge Requests that the client fill out an XEP-0004 data form. XEP-0004 TODO: Insert this document once it is assigned a number ]]>
&NSVER;