Use a validity period of 2 years and 30 days.

Fixes #32.

main.go

@@ -141,7 +141,11 @@ func makeRootCert(key crypto.Signer, filename string) (*x509.Certificate, error)
 		},
 		SerialNumber: serial,
 		NotBefore:    time.Now(),
-		NotAfter:     time.Now().AddDate(100, 0, 0),
+		// Set the validity period to 2 years and 30 days, to satisfy the iOS and
+		// macOS requirements that all server certificates must have validity
+		// shorter than 825 days:
+		// https://derflounder.wordpress.com/2019/06/06/new-tls-security-requirements-for-ios-13-and-macos-catalina-10-15/
+		NotAfter: time.Now().AddDate(2, 30, 0),
 
 		SubjectKeyId:          skid,
 		AuthorityKeyId:        skid,