Message-Based Authentication with WS-Security 
If a WS consumer of an SAP system logs on to a Web service with message-based authentication such as a UsernameToken, a SAML token, or an X.509 certificate, the Internet Communication Framework (ICD) initially performs the logon using the technical user DELAY_L_<SID> that is stored in the ICF. A direct logon with the authentication data contains in the SOAP document is not possible, since the ICF cannot access SOAP data. The report wss_setup creates the DELAY_L_<SID> user, which does not have any authorizations. The report also stores the user password in the secure storage. If the user DELAY_L_<SID> then accesses the WS provider, the provider evaluates, for example, the sent UsernameToken. If the user name and password match, the WS provider performs a user exchange and logs on the user specified in the UsernameToken.
Caution
You need to execute the wss_setup report after the system setup. Otherwise, the user DELAY_L_<SID> and its password will not exist. A logon to a Web Service provider would then fail wiht a 401 header error.

WS Consumer Accesses the WS Provider Using the ICF
The WS consumer wants to access the WS provider and authenticate itself with a UsernameToken.
The ICF cannot evaluate the authentication in the document, but rather requires an HTTP authentication. Therefore it uses the DELAY_L_<SID> user stored in the ICF and its password for the authentication.
The WS provider evaluates the UsernameToken. If the user and password match, it resplaces the user DELAY_L_<SID> with the user specified in the UsernameToken.