feat(alerting): make authentication optional for email provider (#608)

* feat(alerting): Made authentication optional for the email alert provider

* docs: Added  parameter to email alert provider docs

* feat(alerting): Updated email alert to set the LocalName attribute based on the From key

* Updated email provider to disable authentication when no credentials are provided

* Removed `disable-authentication` flag from email provider documentation

* Apply suggestions from code review

---------

Co-authored-by: TwiN <twin@linux.com>

README.md

@@ -471,11 +471,11 @@ endpoints:
 
 #### Configuring Email alerts
 | Parameter                          | Description                                                                                   | Default       |
-|:-----------------------------------|:-------------------------------------------------------------------------------------------|:--------------|
+|:-----------------------------------|:----------------------------------------------------------------------------------------------|:--------------|
 | `alerting.email`                   | Configuration for alerts of type `email`                                                      | `{}`          |
 | `alerting.email.from`              | Email used to send the alert                                                                  | Required `""` |
 | `alerting.email.username`          | Username of the SMTP server used to send the alert. If empty, uses `alerting.email.from`.     | `""`          |
-| `alerting.email.password`          | Password of the SMTP server used to send the alert                                         | Required `""` |
+| `alerting.email.password`          | Password of the SMTP server used to send the alert. If empty, no authentication is performed. | `""`          |
 | `alerting.email.host`              | Host of the mail server (e.g. `smtp.gmail.com`)                                               | Required `""` |
 | `alerting.email.port`              | Port the mail server is listening to (e.g. `587`)                                             | Required `0`  |
 | `alerting.email.to`                | Email(s) to send the alerts to                                                                | Required `""` |

alerting/provider/email/email.go

@@ -49,7 +49,7 @@ func (provider *AlertProvider) IsValid() bool {
 		}
 	}
 
-	return len(provider.From) > 0 && len(provider.Password) > 0 && len(provider.Host) > 0 && len(provider.To) > 0 && provider.Port > 0 && provider.Port < math.MaxUint16
+	return len(provider.From) > 0 && len(provider.Host) > 0 && len(provider.To) > 0 && provider.Port > 0 && provider.Port < math.MaxUint16
 }
 
 // Send an alert using the provider
@@ -66,7 +66,20 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 	m.SetHeader("To", strings.Split(provider.getToForGroup(endpoint.Group), ",")...)
 	m.SetHeader("Subject", subject)
 	m.SetBody("text/plain", body)
-	d := gomail.NewDialer(provider.Host, provider.Port, username, provider.Password)
+	var d *gomail.Dialer
+	if len(provider.Password) == 0 {
+		// Get the domain in the From address
+		localName := "localhost"
+		fromParts := strings.Split(provider.From, `@`)
+		if len(fromParts) == 2 {
+			localName = fromParts[1]
+		}
+		// Create a dialer with no authentication
+		d = &gomail.Dialer{Host: provider.Host, Port: provider.Port, LocalName: localName}
+	} else {
+		// Create an authenticated dialer
+		d = gomail.NewDialer(provider.Host, provider.Port, username, provider.Password)
+	}
 	if provider.ClientConfig != nil && provider.ClientConfig.Insecure {
 		d.TLSConfig = &tls.Config{InsecureSkipVerify: true}
 	}

alerting/provider/email/email_test.go

@@ -18,6 +18,13 @@ func TestAlertDefaultProvider_IsValid(t *testing.T) {
 	}
 }
 
+func TestAlertProvider_IsValidWithNoCredentials(t *testing.T) {
+	validProvider := AlertProvider{From: "from@example.com", Host: "smtp-relay.gmail.com", Port: 587, To: "to@example.com"}
+	if !validProvider.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
 func TestAlertProvider_IsValidWithOverride(t *testing.T) {
 	providerWithInvalidOverrideGroup := AlertProvider{
 		Overrides: []Override{