DeleGate reference manual version 9.9 / Man-In-The-Middle-Mode
If "mitm" is specified, it behaves like "-fcl,-fsv" that is
if SSL is enabled in the client side then SSL on the server side is enabled.
It can be used with a HTTP proxy DeleGate as a "secure proxy" or "SSL-tunnel"
to peep the bidirectional communication in CONNECT method,
relaying it as a usual HTTP applying filters and cache.
("mitm" means "Man-In-The-Middle" mode)
If it is set optional as "STLS=-mitm" then the MITM mode is activated
only when the client specified the server name prefixing with "-mitm."
as "https://-mitm.host.domain/" for "https://host.domain/".