IPsec failover fallsinto two categories:statelessfailover and stateful failover.Statelessfailover uses protocols such as the Hot Standby Router Protocol (HSRP) to provide primary-to-secondary cutover and also allows the active and standby VPN gateways to share a common virtual IP address.

Plug-ins are extensions to the Clientless SSL VPN feature that enable the ASA to handle non-standard applications and Web resources so that they display correctly over a Clientless SSL VPN connection. Plug-ins are software components that the ASA downloads to the remote user's browser. The plug-ins provide support for applications and protocols that are not natively supported by Clientless SSL VPN, such as Java, ActiveX, SSH, Telnet, and RDP. Plug-ins can also provide enhanced functionality and security for Web applications, such as Outlook Web Access and Lotus iNotes.
You can read more about plug-ins and how to configure them in the document [ASDM Book 3: Cisco ASA Series VPN ASDM Configuration Guide, 7.7] 1.

https://www.networkworld.com/article/2288666/chapter-4--common-ipsec-vpn-issues.html

https://www.cisco.com/c/en/us/support/docs/security/flexvpn/116528-config-flexvpn-00.html