L2TP/IPSec client

Has anyone successfully setup a GL.iNet device to act as a L2TP/IPSec client?

Some time ago, I tried various methods using the packages xl2tpd and strongswan-ipsec but was never able to get traffic routed across the tunnel correctly.

Note that the following guides are inadequate, as they only serve to establish an L2TP interface.

What I need is to configure the interface (with username/password) and establish an IPSec tunnel using a pre-shared secret.

Has anyone configured this successfully?

(Note: I am not looking for a discussion of the merits of WireGuard or OpenVPN vs. L2TP. This is a customer requirement, as they have a VPN infrastructure based on L2TP/IPSec server.)