Understanding the SecurityService - NavigationManager injected?

I need an additional service in the SecurityService (defined in SecurityService.cs), so I planned to add a constructor that takes my service as a parameter. I checked the class for avoiding parameter ambiguity and did not expect to find another constructor than the default constructor, because in Startup.cs the SecurityService is added like this:
But there is already a constructor that takes a parameter in SecurityService.cs, but it seems to be never called:
SecurityService(NavigationManager navigationManager)

When it is never called (tested in the debugger), why does the function Logout() from the SecurityService class works at all? I checked in the debugger and the navigationManager attribute is properly initiated and available.
Thanks for helping me to understand the code a bit better to get my customizations right :wink:

Ok, it was way more simpler than I thought, I did not add another constructor, I just extended the existing one to take my own service too as a parameter. Seems like the constructor is called behind the scenes from the service collector. Still grateful for any comment.