3.1.5.1 Determining Message Type

A requestor IP/STS and a relying party process several different types of messages. Upon receipt of a message, they determine its type by inspection of the wa parameter. The wa parameter MUST be included in every message used by this protocol (for further specification, see section 2.2). The wa parameter, and all other protocol-specific parameters, MUST be transported in query string parameters when the protocol message is transported using an HTTP GET. These parameters MUST be transported in the body of the HTTP POST when the protocol message is transported using an HTTP POST. If protocol-specific parameters are included in query string parameters with an HTTP POST, they SHOULD<48> be ignored.

A web browser requestor is not required to understand the types or content of the protocol messages it transports between a requestor IP/STS and a relying party.<49>