$ sudo openvpn client.crssl
Thu Sep 20 16:06:22 2018 OpenVPN 2.4.6 x86_64-pc-linux-gnu [SSL (OpenSSL)] [LZO] [LZ4] [EPOLL] [PKCS11] [MH/PKTINFO] [AEAD] built on Apr 24 2018
Thu Sep 20 16:06:22 2018 library versions: OpenSSL 1.1.1  11 Sep 2018, LZO 2.10
Thu Sep 20 16:06:22 2018 WARNING: No server certificate verification method has been enabled.  See http://openvpn.net/howto.html#mitm for more info.
Thu Sep 20 16:06:22 2018 TCP/UDP: Preserving recently used remote address: [AF_INET]111.222.33.44:1234
Thu Sep 20 16:06:22 2018 Socket Buffers: R=[87380->87380] S=[16384->16384]
Thu Sep 20 16:06:22 2018 Attempting to establish TCP connection with [AF_INET]111.222.33.44:1234 [nonblock]
Thu Sep 20 16:06:24 2018 TCP connection established with [AF_INET]111.222.33.44:1234
Thu Sep 20 16:06:24 2018 TCP_CLIENT link local: (not bound)
Thu Sep 20 16:06:24 2018 TCP_CLIENT link remote: [AF_INET]111.222.33.44:1234
Thu Sep 20 16:06:24 2018 TLS: Initial packet from [AF_INET]111.222.33.44:1234, sid=1c89730a b999cb43
Thu Sep 20 16:06:24 2018 WARNING: this configuration may cache passwords in memory -- use the auth-nocache option to prevent this
Thu Sep 20 16:06:28 2018 VERIFY OK: depth=1, C=CH, ST=Vaud, L=Lausanne, O=Foo, OU=IT, CN=Foo_CA, emailAddress=info@foo.com
Thu Sep 20 16:06:28 2018 VERIFY ERROR: depth=0, error=format error in certificate's notBefore field: C=CH, ST=Vaud, L=Lausanne, O=Foo SA, OU=IT, CN=Foo_SSL_VPN_20180310, emailAddress=info@foo.com
Thu Sep 20 16:06:28 2018 OpenSSL: error:1416F086:SSL routines:tls_process_server_certificate:certificate verify failed
Thu Sep 20 16:06:28 2018 TLS_ERROR: BIO read tls_read_plaintext error
Thu Sep 20 16:06:28 2018 TLS Error: TLS object -> incoming plaintext read error
Thu Sep 20 16:06:28 2018 TLS Error: TLS handshake failed
Thu Sep 20 16:06:28 2018 Fatal TLS error (check_tls_errors_co), restarting
Thu Sep 20 16:06:28 2018 SIGUSR1[soft,tls-error] received, process restarting