How to get the username from the window authentication in Angular?

Recently I have implemented the Angular project and have implemented the window authentication in Web Api. For example:

<security>
<authorization>
<remove users="*" roles="" verbs="" />
<add accessType="Allow" roles="the group that i allow to add " />
</authorization>
</security>

So once I ng serve and run the angular project to open the website it will prompt out the window authentication like this.

Pop out window authentication image

But how can I retrieve the username have entered the window authentication after successful login into the angular website? As I need to get a username for some purpose after login into the angular.