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-possession registration flows and spam prevention mechanisms such as proof-of-work functions.

• The server MUST be able to present multiple challenges to the client.
• The server SHOULD be able reduce account registration spam.
• The server MAY present a challenge that requires the user to complete a step out-of-band.
• A client SHOULD be able to register an account without requiring the user to leave the client.
• A client MUST be able to use the same mechanism to register an account and to recover a forgotten password (subject to server policy).
• A client MUST be able to register with a server as well as external components.

• As a server operator, I want to prevent individual spammers from registering many accounts so I require registrants to perform a proof-of-work function before registration is completed.
• As a server operator I want to prevent bots from registering accounts so I require that registrants submit a form which requires user interaction.
• As a user I do not want to lose access to my account if I forget my password, so I provide my email and telephone number in response to the servers data form.
• As a server operator I do not want users to accidentally add an incorrect recovery address so I send an email with a unique link to the indicated account and require that they click the link before registration can continue.
• As a server operator I want to prevent SPIM using a proof-of-possession protocol so I present the user with a form asking for a mobile phone number and then send a verification code to that number via SMS and show another form requesting the verification code.

A client selects the registration or recovery feature for negotiation by replying with an element of the same name and namespace. The element MUST contain a <flow> element that MUST have an "id" attribute matching one of the flows advertised by the server. For example, to select the "Verify by Phone Call" registration flow from the previous example, the client would reply with:

If the client is initiating registration or recovery after a stream has already been initiated it uses the same registration element wrapped in an IQ of type "set".

The server then replies to the IQ or feature selection with a challenge. If replying to an IQ, the challenge must be wrapped in an IQ of type "result". 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:

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 cancellation 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:

If after receiving a challenge or response a client or server 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 client or server that registration is complete. This is the same as submitting a data form of type 'cancel' in response to a data form challenge.

If the IQ based registration or recovery flow is being used and the server wishes to cancel the flow, it MAY respond to any IQ from the client with the cancel element and type "result".

If the client successfully completes all required challenges during stream negotiation the server MUST 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.

If the IQ based flow is being used and the server wishes to indicate success it sends an empty IQ response of type "result".

When providing instructions in a data form, or in the name element of a registration or recovery flow, 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-possession 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;.