Specifying SAML Assertions 
When using the Single Sign-On with SAML (Authentication in Message) authentication method, you can specify SAML assertion.
It is optional to specify SAML assertion and is only possible when the following conditions are fulfilled:
Symmetrical Message Signature/Encryption or HTTPS (Transport Channel Security) has been set for comunication security.
For receiver channels: Non-local calls set and the assigned communication component references an SAP system (see Target Client under Technical Transport Settings).
Procedure
Select SAML assertion under Security Token Service Settings in the SAML Assertion field using input help.
Note
The assertions available are stored in the SAP system in the WSS_STS_URL_TAB table (you can display this, for example, using transaction SM30).
More information: Configuring SSO/STS Scenario SAML Holder-of-key in the Provider System AS ABAP