ElasticsearchWriter: actually verify TLS server certificates

And add a new option insecure_noverify to explicitly disable it if desired.

doc/09-object-types.md

@@ -1238,6 +1238,7 @@ Configuration Attributes:
   username                  | String                | **Optional.** Basic auth username if Elasticsearch is hidden behind an HTTP proxy.
   password                  | String                | **Optional.** Basic auth password if Elasticsearch is hidden behind an HTTP proxy.
   enable\_tls               | Boolean               | **Optional.** Whether to use a TLS stream. Defaults to `false`. Requires an HTTP proxy.
+  insecure\_noverify        | Boolean               | **Optional.** Disable TLS peer verification.
   ca\_path                  | String                | **Optional.** Path to CA certificate to validate the remote host. Requires `enable_tls` set to `true`.
   cert\_path                | String                | **Optional.** Path to host certificate to present to the remote host for mutual verification. Requires `enable_tls` set to `true`.
   key\_path                 | String                | **Optional.** Path to host key to accompany the cert\_path. Requires `enable_tls` set to `true`.

lib/perfdata/elasticsearchwriter.cpp

@@ -632,6 +632,18 @@ OptionalTlsStream ElasticsearchWriter::Connect()
 				<< "TLS handshake with host '" << GetHost() << "' on port " << GetPort() << " failed.";
 			throw;
 		}
+
+		if (!GetInsecureNoverify()) {
+			if (!tlsStream.GetPeerCertificate()) {
+				BOOST_THROW_EXCEPTION(std::runtime_error("Elasticsearch didn't present any TLS certificate."));
+			}
+
+			if (!tlsStream.IsVerifyOK()) {
+				BOOST_THROW_EXCEPTION(std::runtime_error(
+					"TLS certificate validation failed: " + std::string(tlsStream.GetVerifyError())
+				));
+			}
+		}
 	}
 
 	return std::move(stream);

lib/perfdata/elasticsearchwriter.ti

@@ -29,6 +29,9 @@ class ElasticsearchWriter : ConfigObject
 	[config] bool enable_tls {
 		default {{{ return false; }}}
 	};
+	[config] bool insecure_noverify {
+		default {{{ return false; }}}
+	};
 	[config] String ca_path;
 	[config] String cert_path;
 	[config] String key_path;