fix(snmp3): when using SNMPv3, userName always needs to be set. (#68)

* When using SNMPv3, userName always needs to be set.

See https://tools.ietf.org/html/rfc3414#section-3.1, point 7: userName is set into the trap even when securityLevel = NoAuthNoPriv
Dependency "github.com/k-sone/snmpgo" is returning an error when username is not set

* feat(snmp3): Configure userName even when authentication is disabled.

configuration/configuration.go

@@ -125,6 +125,7 @@ func ParseConfiguration(args []string) (*SNMPNotifierConfiguration, error) {
 	}
 
 	if !isV2c {
+		trapSenderConfiguration.SNMPAuthenticationUsername = *snmpAuthenticationUsername
 		trapSenderConfiguration.SNMPSecurityEngineID = *snmpSecurityEngineID
 		trapSenderConfiguration.SNMPContextEngineID = *snmpContextEngineID
 		trapSenderConfiguration.SNMPContextName = *snmpContextName
@@ -141,7 +142,6 @@ func ParseConfiguration(args []string) (*SNMPNotifierConfiguration, error) {
 	if *snmpAuthenticationEnabled {
 		trapSenderConfiguration.SNMPAuthenticationEnabled = *snmpAuthenticationEnabled
 		trapSenderConfiguration.SNMPAuthenticationProtocol = *snmpAuthenticationProtocol
-		trapSenderConfiguration.SNMPAuthenticationUsername = *snmpAuthenticationUsername
 		trapSenderConfiguration.SNMPAuthenticationPassword = *snmpAuthenticationPassword
 	}
 	if *snmpPrivateEnabled {

configuration/configuration_test.go

@@ -157,10 +157,11 @@ var tests = []Test{
 				Severities:      []string{"critical", "error", "warning", "info"},
 			},
 			trapsender.Configuration{
-				SNMPVersion:         "V3",
-				SNMPDestination:     "127.0.0.2:163",
-				SNMPRetries:         4,
-				ExtraFieldTemplates: make(map[string]template.Template),
+				SNMPVersion:                "V3",
+				SNMPDestination:            "127.0.0.2:163",
+				SNMPRetries:                4,
+				SNMPAuthenticationUsername: "username_v3",
+				ExtraFieldTemplates:        make(map[string]template.Template),
 			},
 			httpserver.Configuration{
 				WebListenAddress: ":1234",