Don't request certs if date isn't set properly

[grischard]

I use ssl-proxy on a robot. Since it doesn't have a real-time clock, it syncs its time over ntp after booting.

To avoid letsencrypt rate limiting, ssl-proxy should sanity check to make sure that the date is set to after 1970 before requesting certificates.

See also: golang/go#28201

A tragedy in log file format on machine reboot:

1970/01/01 00:00:09 Assuming -to URL is using http://
1970/01/01 00:00:09 Proxying calls from https://[::]:443 (SSL/TLS) to http://127.0.0.1:8000
1970/01/01 00:00:09 Domain specified, using LetsEncrypt to autogenerate and serve certs for foo.example.com
1970/01/01 00:00:09 Also redirecting https requests on port 80 to https requests on foo.example.com
1970/01/01 00:00:19 http: TLS handshake error from [fe80::1234]:57129: acme/autocert: missing certificate
1970/01/01 00:00:19 http: TLS handshake error from [fe80::1234]:57128: Get "https://acme-v02.api.letsencrypt.org/directory": x509: certificate has expired or is not yet valid: current time 1970-01-01T00:00:18Z is before 2022-04-26T22:21:59Z
1970/01/01 00:00:19 http: TLS handshake error from [fe80::1234]:57130: acme/autocert: missing certificate
1970/01/01 00:00:19 http: TLS handshake error from [fe80::1234]:57131: acme/autocert: missing certificate
1970/01/01 00:00:20 http: TLS handshake error from [fe80::1234]:57132: acme/autocert: missing certificate
1970/01/01 00:00:20 http: TLS handshake error from [fe80::1234]:57133: acme/autocert: missing certificate
1970/01/01 00:00:20 http: TLS handshake error from [fe80::1234]:57134: acme/autocert: missing certificate
1970/01/01 00:00:20 http: TLS handshake error from [fe80::1234]:57135: acme/autocert: missing certificate
1970/01/01 00:00:23 http: TLS handshake error from [fe80::1234]:57138: acme/autocert: missing certificate
1970/01/01 00:00:23 http: TLS handshake error from [fe80::1234]:57136: acme/autocert: missing certificate
1970/01/01 00:00:23 http: TLS handshake error from [fe80::1234]:57137: acme/autocert: missing certificate
1970/01/01 00:00:23 http: TLS handshake error from [fe80::1234]:57139: acme/autocert: missing certificate
1970/01/01 00:00:23 http: TLS handshake error from [fe80::1234]:57141: acme/autocert: missing certificate
1970/01/01 00:00:23 http: TLS handshake error from [fe80::1234]:57140: acme/autocert: missing certificate
2022/05/02 03:56:00 http: TLS handshake error from [fe80::1234]:57142: acme/autocert: missing certificate
2022/05/02 03:56:00 http: TLS handshake error from [fe80::1234]:57143: acme/autocert: missing certificate
2022/05/02 03:56:00 http: TLS handshake error from [fe80::1234]:57144: acme/autocert: missing certificate
2022/05/02 03:56:00 http: TLS handshake error from [fe80::1234]:57145: acme/autocert: missing certificate
2022/05/02 03:56:05 http: TLS handshake error from [fe80::1234]:57146: acme/autocert: missing certificate
2022/05/02 03:56:05 http: TLS handshake error from [fe80::1234]:57147: acme/autocert: missing certificate
2022/05/02 03:56:06 http: TLS handshake error from [fe80::1234]:57148: acme/autocert: missing certificate
2022/05/02 03:56:06 http: TLS handshake error from [fe80::1234]:57149: acme/autocert: missing certificate
2022/05/02 03:56:08 http: TLS handshake error from [fe80::1234]:57150: acme/autocert: missing certificate
2022/05/02 03:56:08 http: TLS handshake error from [fe80::1234]:57151: acme/autocert: missing certificate
2022/05/02 03:56:12 http: TLS handshake error from [fe80::1234]:57152: acme/autocert: missing certificate
2022/05/02 03:56:12 http: TLS handshake error from [fe80::1234]:57153: acme/autocert: missing certificate
2022/05/02 03:56:15 http: TLS handshake error from [fe80::1234]:57181: acme/autocert: missing certificate
2022/05/02 03:56:15 http: TLS handshake error from [fe80::1234]:57182: acme/autocert: missing certificate
2022/05/02 03:56:16 http: TLS handshake error from [fe80::1234]:57184: acme/autocert: missing certificate
2022/05/02 03:56:16 http: TLS handshake error from [fe80::1234]:57185: acme/autocert: missing certificate
2022/05/02 03:56:18 http: TLS handshake error from [fe80::1234]:57186: acme/autocert: missing certificate
2022/05/02 03:56:18 http: TLS handshake error from [fe80::1234]:57187: acme/autocert: missing certificate
2022/05/02 03:56:22 http: TLS handshake error from [fe80::1234]:57188: acme/autocert: missing certificate
2022/05/02 03:56:22 http: TLS handshake error from [fe80::1234]:57189: acme/autocert: missing certificate
2022/05/02 03:56:29 http: TLS handshake error from [fe80::1234]:57190: acme/autocert: missing certificate
2022/05/02 03:56:29 http: TLS handshake error from [fe80::1234]:57191: acme/autocert: missing certificate
2022/05/02 03:56:29 http: TLS handshake error from [fe80::1234]:57192: acme/autocert: missing certificate
2022/05/02 03:56:29 http: TLS handshake error from [fe80::1234]:57194: acme/autocert: missing certificate
2022/05/02 03:56:29 http: TLS handshake error from [fe80::1234]:57193: acme/autocert: missing certificate
2022/05/02 03:56:29 http: TLS handshake error from [fe80::1234]:57195: acme/autocert: missing certificate
2022/05/02 03:56:30 http: TLS handshake error from [fe80::1234]:57196: acme/autocert: missing certificate
2022/05/02 03:56:30 http: TLS handshake error from [fe80::1234]:57197: acme/autocert: missing certificate
2022/05/02 03:56:30 http: TLS handshake error from [fe80::1234]:57198: acme/autocert: missing certificate
2022/05/02 03:56:30 http: TLS handshake error from [fe80::1234]:57199: acme/autocert: missing certificate
2022/05/02 03:56:32 http: TLS handshake error from [fe80::1234]:57201: acme/autocert: missing certificate
2022/05/02 03:56:32 http: TLS handshake error from [fe80::1234]:57202: acme/autocert: missing certificate
2022/05/02 03:56:32 http: TLS handshake error from [fe80::1234]:57203: acme/autocert: missing certificate
2022/05/02 03:56:32 http: TLS handshake error from [fe80::1234]:57204: acme/autocert: missing certificate
2022/05/02 03:56:36 http: TLS handshake error from [fe80::1234]:57216: acme/autocert: missing certificate
2022/05/02 03:56:36 http: TLS handshake error from [fe80::1234]:57217: acme/autocert: missing certificate
2022/05/02 03:56:36 http: TLS handshake error from [fe80::1234]:57218: acme/autocert: missing certificate
2022/05/02 03:56:36 http: TLS handshake error from [fe80::1234]:57221: acme/autocert: missing certificate
2022/05/02 03:56:41 http: TLS handshake error from [fe80::1234]:57234: acme/autocert: missing certificate
2022/05/02 03:56:41 http: TLS handshake error from [fe80::1234]:57235: acme/autocert: missing certificate
2022/05/02 03:56:42 http: TLS handshake error from [fe80::1234]:57236: acme/autocert: missing certificate
2022/05/02 03:56:42 http: TLS handshake error from [fe80::1234]:57237: acme/autocert: missing certificate
2022/05/02 03:56:44 http: TLS handshake error from [fe80::1234]:57238: acme/autocert: missing certificate
2022/05/02 03:56:44 http: TLS handshake error from [fe80::1234]:57239: acme/autocert: missing certificate
2022/05/02 03:56:48 http: TLS handshake error from [fe80::1234]:57240: acme/autocert: missing certificate
2022/05/02 03:56:48 http: TLS handshake error from [fe80::1234]:57241: acme/autocert: missing certificate
2022/05/02 04:01:53 http: TLS handshake error from [fe80::1234]:57336: acme/autocert: missing certificate
2022/05/02 04:01:53 http: TLS handshake error from [fe80::1234]:57244: acme/autocert: missing certificate
2022/05/02 04:01:53 http: TLS handshake error from [fe80::1234]:57329: acme/autocert: missing certificate
2022/05/02 04:01:53 http: TLS handshake error from [fe80::1234]:57478: acme/autocert: missing certificate
2022/05/02 04:01:53 http: TLS handshake error from [fe80::1234]:57247: acme/autocert: missing certificate
2022/05/02 04:01:53 http: TLS handshake error from [fe80::1234]:57242: 429 urn:ietf:params:acme:error:rateLimited: Error creating new order :: too many certificates (5) already issued for this exact set of domains in the last 168 hours: foo.example.com: see https://letsencrypt.org/docs/rate-limits/
2022/05/02 04:01:53 http: TLS handshake error from [fe80::1234]:57273: acme/autocert: missing certificate