If Romeo is an XMPP user, he can create an out-of-band link (URI) which allows Juliet to:

1. Download an XMPP client (if needed).
2. Optionally register an account with Romeo's server (if permitted by the server rules), or with a public server.
3. Establish a mutual presence subscription between Romeo and Juliet.

The process is designed to automatically skip steps that Juliet already completed, to make the overall experience as smooth as possible.

If Romeo is an administrator of an XMPP server, he can create an out-of-band link (URI) which allows Juliet to:

1. Download an XMPP client (if needed).
2. Register an account on Romeo's server with a user name defined by Romeo and a password not known to Romeo.
3. Establish a mutual presence subscription between Romeo and Juliet.

A user can execute the 'invite' command to obtain a new invitation link with a unique invitation token.

The token should be unique, sufficiently long and generated by a strong random number generator.

A server MUST provide the uri field which contains an XMPP URI of the following format:

The ibr query component in the XMPP URI indicates that the invitee is allowed to create an account on Romeo's server, using the 'preauth' token. If the server does not support or allow in-band registration for invited users, the server MUST omit the ibr query component.

Additionally, the server SHOULD provide the landing-url field which contains an HTTPS URL of a web-based landing page as described in &xep0379; § 3.3. The URL format may differ from the example shown here depending on where the landing page is hosted.

If the server omits the landing-page field, Romeo's client SHOULD generate an appropriate landing page URL hosted by the client developer or a trusted third party.

A server MAY provide a field which provides the expiration date of the generated token. The expiration date MUST conform to the DateTime profile specified in &xep0082;. If the field is not provided, the token does not expire.

Romeo's client should provide adequate means to export the landing-page URL, possibly accompanied with a short description and the expire information, so that Romeo can share it with Juliet by other means than XMPP, like e-mail or a QR code.

The landing page that the generated URL points to should correspond to the format described in XEP-0379 §3.3, and it needs to convey the following information:

• A short text that this is an XMPP invitation from Romeo.
• A client recommendation (based on the detected web browser/OS) with download links.
• A prominent button that activates the encoded xmpp: link.

If the landing page is hosted by Romeo's server, the server MAY display additional information based on the supplied TOKEN value, like the name of the inviter or validity information.

If Juliet does not have an XMPP client installed, she will not be able to open the xmpp: link from the invitation page. For this case, the landing page needs to indicate that a client must be installed first, and that the link will not work as intended without. The automatic installation of an appropriate IM client when a user clicks on an xmpp: is outside of the scope of this document.

With an XMPP client installed, Juliet can open the xmpp: link and have the client process it appropriately, as follows:

If Romeo is the administrator of an XMPP server, he might want to ensure that Juliet obtains an account on this server, with a username defined either by Romeo or by Juliet, and in a way that does not require the out-of-band communication of user passwords.

TODO: description of overall process steps, design motivation.

A server MAY require a username to be specified for account creation. In this case, the server MUST add the <required/> element to the username field. The username MUST be a valid localpart as defined in &rfc6122; §2.3.

The server's response for account creation is the same as for user invitation except for the format of the uri field which contains an XMPP URI of the following format:

If no username was specified during the account creation process, the local part of the JID in the XMPP URI is omitted by the server which results in the following format:

TODO: note about sensitivity of TOKEN

In order to allow invited users to register on a server, the registration processs as defined in &xep0077; needs to be extended. The invited user's client MUST add a <preauth> element in the 'TODO' namespace to the 'jabber:iq:register' query in order to inform the server that it wants to perform Pre-Authenticated IBR:

If the server supports and is ready to perform Pre-Authenticated IBR, it MUST add a <token> element to the response (TODO: 'token' or 'preauth'?):

After the invitee has successfully registered on the inviter's server and roster subscription is enabled for account creation, the server MUST use roster pushes as defined in &rfc6121; §2.1.6 in order to inform the inviter about the invitee's new account without the need to reconnect.

If the inviter's server does not support user invitation, the client application SHOULD silently fall back to &xep0379; for a good user experience.

If a username was specified during the account creation process, the server SHOULD NOT create an account on the server until the invitee actually registers it with the corresponding token. The server MUST reserve the username at least until the corresponding token expires.

If the invitee opens an invitation URI with ibr=y and chooses to create a new account, the client SHOULD pre-fill the inviter JID's domain part as the new account's domain. The client MAY provide a mechanism to enter or choose a different server, though.