TCallback = class(TInvokableClass, Callback)
  public
    function sendResponse(const id: string; const oid: string; const response: string): Status; stdcall;
  end;

 TSOAPCredentials = class(TSoapHeader)
 private
   fMessageID:string;
 public
   constructor Create; overload; override;
   constructor Create(AMessageID:string);  overload;

   function ObjectToSOAP(RootNode, ParentNode: IXMLNode;
                            const ObjConverter: IObjConverter;
                            const NodeName, NodeNamespace, ChildNamespace: InvString; ObjConvOpts: TObjectConvertOptions;
                            out RefID: InvString): IXMLNode; override;
 end;

 
initialization
  InvRegistry.RegisterInvokableClass(TCallback);
  InvRegistry.RegisterHeaderClass(TypeInfo(TCallback), TSOAPCredentials);
  InvRegistry.RegisterDefaultSOAPAction(TypeInfo(TCallback), 'sendResponse');