Microsoft.AspNetCore.Session
Microsoft.AspNetCore.Http.Extensions

// 添加一个内存缓存
services.AddDistributedMemoryCache();
services.AddSession(options =>
{
    // 设置10秒钟Session过期来测试
    options.IdleTimeout = TimeSpan.FromSeconds(10);
    options.Cookie.HttpOnly = true;
});

app.UseSession();

HttpContext.Session.SetString("param", str);
string value = HttpContext.Session.GetString("param");

public class SessionTestClass
{
    private readonly IHttpContextAccessor _httpContextAccessor;
    private ISession _session => _httpContextAccessor.HttpContext.Session;

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

    public void Set()
    {
        _session.SetString("code", "123456");
    }

    public void Get()
    {
        string code = _session.GetString("code");
    }
}

public static class SessionExtensions
{
    public static void SetObjectAsJson(this ISession session, string key, object value)
    {
        session.SetString(key, JsonConvert.SerializeObject(value));
    }

    public static T GetObjectFromJson<T>(this ISession session, string key)
    {
        var value = session.GetString(key);

        return value == null ? default(T) : JsonConvert.DeserializeObject<T>(value);
    }
}

var myTestObject = new MyTestClass();
HttpContext.Session.SetObjectAsJson("SessionTest", myTestObject);
var myComplexObject = HttpContext.Session.GetObjectFromJson<MyClass>("SessionTest");