3.3.4 Higher Layer Triggered Events

Protocol messages are exchanged between a requestor IP/STS and a relying party. The only function of the web browser requestor with respect to the protocol is to transport these messages. The web browser requestor can be triggered to begin protocol message exchange by receipt of an HTTP/1.1 302 found that includes a location directive, or an HTTP/1.1 200 OK that includes a form with method set to POST.