public void ConfigureServices(IServiceCollection services)
{
 services.AddCors(options =>
    {
        options.AddPolicy("CorsPolicy",
            builder => builder
                .AllowAnyOrigin()
                .AllowAnyMethod()
                .AllowAnyHeader()
                .AllowCredentials()
                );
    });

    .....

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            app.UseCors(policyName: "CorsPolicy");

            ....

[Route("api/[controller]")]
    [EnableCors("CorsPolicy")]
    public class ManageUsersController : Controller
    { ...

loginByPortal(credentials: Credentials): Observable<userLoginViewmodel> {
    const headers = new HttpHeaders({ 'Content-Type': 'application/json' });
    return this.http
      .post(`${this.appConfig.apiEndpoint}/Account/LoginByPortal`, credentials,
       { headers: headers, withCredentials: true /* For CORS */ })
      .map(response => response || {})
      .catch((error: HttpErrorResponse) => Observable.throw(error));
  }