procedure TForm1.Button1Click(Sender: TObject);
begin
(HTTPRIO1 as ClientSoap).Logon('login','pass','1.1','1.1');
end;

POST /ClientWebService/Client.asmx HTTP/1.1
Host: 192.168.1.1
Content-Type: text/xml; charset=utf-8
Content-Length: length
SOAPAction: "http://неважно/Logon"

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <Logon xmlns="неважно">
      <Login>string</Login>
      <Password>string</Password>
      <ApplicationName>string</ApplicationName>
      <WorkstationName>string</WorkstationName>
    </Logon>
  </soap:Body>
</soap:Envelope>

HTTP/1.1 200 OK
Content-Type: text/xml; charset=utf-8
Content-Length: length

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Header>
    <SecurityHeader xmlns="неважно">
      <SessionGuid>guid</SessionGuid>
    </SecurityHeader>
  </soap:Header>
  <soap:Body>
    <LogonResponse xmlns="неважно">
      <LogonResult namespace="" tableTypeName="">xmlxml</LogonResult>
    </LogonResponse>
  </soap:Body>
</soap:Envelope>

function  Logon(const Login: string; const Password: string; const ApplicationName: string; const WorkstationName: string): LogonResult; stdcall;
procedure Logoff; stdcall;

POST /неважно/Client.asmx HTTP/1.1
Host: 192.168.1.1
Content-Type: text/xml; charset=utf-8
Content-Length: length
SOAPAction: "http://неважно/Logoff"

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Header>
    <SecurityHeader xmlns="неважно">
      <SessionGuid>guid</SessionGuid>
    </SecurityHeader>
  </soap:Header>
  <soap:Body>
    <Logoff xmlns="неважно" />
  </soap:Body>
</soap:Envelope>

HTTP/1.1 200 OK
Content-Type: text/xml; charset=utf-8
Content-Length: length

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Header>
    <SecurityHeader xmlns="неважно">
      <SessionGuid>guid</SessionGuid>
    </SecurityHeader>
  </soap:Header>
  <soap:Body>
    <LogoffResponse xmlns="http://неважно" />
  </soap:Body>
</soap:Envelope>