asp.net core authentication using firebase

I'm trying to create an asp.net core api that verifies the user Identity using firebase authentication, and store all his data in internal postgreSQL data base - including rules for authorization (such as Admin and other custom rules).

I Managed to verify the token using the firebase nuget package:

 public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<ApplicationDBContext>(options => options.UseNpgsql(
           Configuration.GetConnectionString("DeafultConnectionString")));

        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        services.AddFirebaseAuthentication(Configuration.GetSection("FirebaseAuth:issuer").Value,
            Configuration.GetSection("FirebaseAuth:audience").Value);

      //  services.AddIdentity<Auth.ApplicationUser, IdentityRole>().AddEntityFrameworkStores<ApplicationDBContext>();
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseHsts();
        }

        app.UseAuthentication();
        app.UseHttpsRedirection();
        app.UseMvc();
    }
}

and this works perfectly fine! I'm trying to understand how I connect my database to store the user details - but I can't uderstand how it's done. any help?