The agreement reference.
This property holds a value identifying the agreement between the two parties. The agreement is made outside the scope of the request and response and governs details about the interaction including reply mode, signing and encryption options, etc.
The value of this property should be set to a mutually agreed upon identifier. Both parties will use this value know what the expected requirements are for a particular request or response.
The format of this value is typically a URI, such as "http://mycompany.com/agreement_01" but can be any unique string that both parties are configured to accept. Another common format is the concatenation of the AS4From and AS4To values.
This value corresponds to the ebMS element "eb:Messaging/eb:UserMessage/eb:CollaborationInfo/eb:AgreementRef"