The auto-signon command is a single sign-on method for users of clientless SSL VPN sessions.
It passes the login credentials (username and password) to internal servers for authentication using NTLM authentication, basic authentication, or both. Multiple auto-signon commands can be entered and are processed according to the input order (early commands take precedence).
https://www.cisco.com/c/en/us/td/docs/security/asa/asa916/configuration/vpn/asa-916-vpn- config/webvpn-configure-policy-groups.html#ID-2439-00001438