I happened to be reviewing the 10th draft of the OpenID 2.0 Authentication spec, when I noticed this nugget in section 5.2.1 of the draft:

[HTTP redirect] method is deprecated as of OpenID Authentication version 2.0 though is still required for implementation to aide in backwards compatibility.

In place of the HTTP redirect used by OpenID 1.1, is this, in section 5.2.2:

A mapping of keys to values can be transferred by returning an HTML page to the User-Agent that contains an HTML form element. Form submission MAY be automated using JavaScript.

The <form> element’s “action” attribute value MUST be the URL of the receiving Web site. Each Key-Value pair MUST be included in the form as an <input> element.