Thank you contacting Syncfusion support.
Based on provided information, we understood that you need to add a custom button in Title bar to display sign in, but currently we do not have a support to add a control in the Title bar. We already have logged a feature request for this and we will implement this in any of our upcoming releases. You can also communicate with us regarding the open features any time using our Feature Report page.
If you have any more specification/suggestions to the feature request, you can add it as a comment in the portal and cast your vote to make it count.