feat(ssh): Support authless SSH health check (#956)

* Feature + Test +  Documentation: added no-auth ssh health cheack feature, changed documentation to fit new behavior, added ssh test cases.

* Refactor: refactored authenticate field to infer from username and password insted of specifying it inside config.

* Refactor: removed non used field.

* Refactor: changed error, removed spaces.

* Refactor: added comments.

config/endpoint/endpoint.go

@@ -363,6 +363,18 @@ func (e *Endpoint) call(result *Result) {
 		}
 		result.Duration = time.Since(startTime)
 	} else if endpointType == TypeSSH {
+		// If there's no username/password specified, attempt to validate just the SSH banner
+		if len(e.SSHConfig.Username) == 0 && len(e.SSHConfig.Password) == 0 {
+			result.Connected, result.HTTPStatus, err =
+				client.CheckSSHBanner(strings.TrimPrefix(e.URL, "ssh://"), e.ClientConfig)
+			if err != nil {
+				result.AddError(err.Error())
+				return
+			}
+			result.Success = result.Connected
+			result.Duration = time.Since(startTime)
+			return
+		}
 		var cli *ssh.Client
 		result.Connected, cli, err = client.CanCreateSSHConnection(strings.TrimPrefix(e.URL, "ssh://"), e.SSHConfig.Username, e.SSHConfig.Password, e.ClientConfig)
 		if err != nil {

config/endpoint/ssh/ssh.go

@@ -19,6 +19,10 @@ type Config struct {
 
 // Validate the SSH configuration
 func (cfg *Config) Validate() error {
+	// If there's no username and password, this endpoint can still check the SSH banner, so the endpoint is still valid
+	if len(cfg.Username) == 0 && len(cfg.Password) == 0 {
+		return nil
+	}
 	if len(cfg.Username) == 0 {
 		return ErrEndpointWithoutSSHUsername
 	}

config/endpoint/ssh/ssh_test.go

@@ -7,10 +7,8 @@ import (
 
 func TestSSH_validate(t *testing.T) {
 	cfg := &Config{}
-	if err := cfg.Validate(); err == nil {
-		t.Error("expected an error")
-	} else if !errors.Is(err, ErrEndpointWithoutSSHUsername) {
-		t.Errorf("expected error to be '%v', got '%v'", ErrEndpointWithoutSSHUsername, err)
+	if err := cfg.Validate(); err != nil {
+		t.Error("didn't expect an error")
 	}
 	cfg.Username = "username"
 	if err := cfg.Validate(); err == nil {