User Name and Password 

The SAP system can make use of various single sign-on options. However, many customers still use a separate user name and password for logging on to SAP. When designing SAP .NET Connector applications, we recommend to avoid scenarios where a single user ID is used to connect to the SAP system. In general, all users of the SAP system whether through SAPGUI or the SAP. NET Connector must be licensed. For that reason, it is preferable to ask the user for their SAP user name and password as part of your application or to make use of one of the single sign-on options.

A very good option for user name and password authentication is the SAP Login form. If you are writing an ASP .NET application this provides you with a forms-based authentication and the necessary plumbing for both session and cookie based single sign-on after the first time visiting the form.