Лог nginx
2017/05/01 17:54:30 [error] 20248#0: *27 SSL_do_handshake() failed (SSL: error:14094418:SSL routines:SSL3_READ_BYTES:tlsv1 alert unknown ca:SSL alert number 48) while SSL handshaking to upstream, client: ip-client, server: server-in-inet, request: "POST / HTTP/1.1", upstream: "https://IP-adres-server-in-inet:443/Exec", host: "server-in-inet"