Fix error in config service

src/configuration/config.service.ts

@@ -11,9 +11,12 @@ export class ConfigService {
     this._config.smtpConfig.port = process.env.SMTP_PORT;
 
     if (process.env.SMTP_USER && process.env.SMTP_PASSWORD) {
-      this._config.smtpConfig.auth = {
-        user: process.env.SMTP_USER,
-        pass: process.env.SMTP_PASSWORD,
+      this._config.smtpConfig = {
+        ...this._config.smtpConfig,
+        auth: {
+          user: process.env.SMTP_USER,
+          pass: process.env.SMTP_PASSWORD,
+        },
       };
     }
     this._config.mailSubjectPrefix = process.env.MAIL_SUBJECT_PREFIX;