1. 确认在 Startup.cs 中是否已配置会话：

public void ConfigureServices(IServiceCollection services)
{
    ...

    services.AddSession();
    services.AddMvc();
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    ...

    app.UseSession();
    app.UseMvc();
}

2. 在 API 控制器中添加 Session

[Route("api/[controller]")]
public class TestController : Controller
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public TestController(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    [HttpGet("[action]")]
    public void SetSession(string key, string value)
    {
        _httpContextAccessor.HttpContext.Session.SetString(key, value);
    }

    [HttpGet("[action]")]
    public string GetSession(string key)
    {
        return _httpContextAccessor.HttpContext.Session.GetString(key);
    }
}

3. 确认在 Angular 服务中配置了 withCredentials

@Injectable()
export class ApiService {
  private getUrl(path: string): string {
    return `${environment.apiUrl}/${path}`;
  }

  constructor(private http: HttpClient) {}

  public post(path: string, body: any): Observable {
    const headers = new HttpHeaders().set('Content-Type', 'application/json');
    return this.http.post(this.getUrl(path), body, { headers, withCredentials: true });
  }

  public get(path: string): Observable {
    return this.http.get(this.getUrl(path), { withCredentials: true });
  }
}

4. 确认在初始化时配置了 Cookie 策略：

services.ConfigureApplicationCookie(options =>
{
    options.Cookie.HttpOnly = true;
    options.ExpireTimeSpan = TimeSpan.FromMinutes(30);
    options.Cookie.SecurePolicy = CookieSecurePolicy.None;
    options.Cookie.SameSite = SameSiteMode.None;
    options.LoginPath = "/";
    options.LogoutPath = "/";
});

通过以上步骤，Angular 发出调用请求后，ASP.NET Core 会话就可以正确地获取了。