[Elastic Agent] Add check for URL set when cert and cert key. (elasti…

…c#24904)

* Add check for URL set when cert and cert key.

* Add changelog.

x-pack/elastic-agent/CHANGELOG.next.asciidoc

@@ -46,6 +46,7 @@
 - Verify communication to Kibana before updating Fleet client. {pull}24489[24489]
 - Fix nil pointer when null is generated as list item. {issue}23734[23734]
 - Add support for filestream input. {pull}24820[24820]
+- Add check for URL set when cert and cert key. {pull}24904[24904]
 
 ==== New features
 

x-pack/elastic-agent/pkg/agent/cmd/enroll_cmd.go

@@ -296,6 +296,10 @@ func (c *enrollCmd) prepareFleetTLS() error {
 		c.options.URL = fmt.Sprintf("https://%s:%d", hostname, port)
 		c.options.CAs = []string{string(ca.Crt())}
 	}
+	// running with custom Cert and CertKey; URL is required to be set
+	if c.options.URL == "" {
+		return errors.New("url is required when a certificate is provided")
+	}
 	return nil
 }