.NET微信网页开发之通过UnionID机制，解决用户在不同公众号，或在公众号、移动应用之间帐号统一问题

//授权入口
public ActionResult WxLogin()
{
//异步跳转地址
var loginUrl = "http://" + Request.Url.Authority + Url.Action("WxRegisterAndLogin") ;
return Redirect("https://open.weixin.qq.com/connect/oauth2/authorize?appid=" + appid + "&redirect_uri=" + Url.Encode(loginUrl) + "&response_type=code&scope=snsapi_userinfo&state=state#wechat_redirect");
}

/// <summary>
/// 微信登录注册（通过unionid来判断之前是否已经存在同一个工作平台注册过的账号，假如存在的话则关联起来，不存在注册一个新的账号）
/// </summary>
/// <param name="code">获取用户凭证换取用户网页授权</param>
/// <param name="ReturnUrl">跳转地址</param>
/// <returns></returns>
public async Task<ActionResult> WxRegisterAndLogin(string code, string ReturnUrl = "")
{
try
{
//登录成功后跳转的地址
string url=ReturnUrl;
//通过Code以及微信appscrect和wxappid换取网页授权access_token和用户oppenid
HttpClient webClient = new HttpClient();
var  jsonString = await (await webClient.GetAsync("https://api.weixin.qq.com/sns/oauth2/access_token?appid=" +公众号appid+ "&secret=" + 公众号AppSecret + "&code=" + code + "&grant_type=authorization_code")).Content.ReadAsStringAsync();
//异步获取的用户oppenid和access_token
var  jsonOAuthorObj = JsonConvert.DeserializeObject(jsonString, new { access_token = "", openid = "" }.GetType());
if (jsonOAuthorObj.openid == null)
{
return Content(jsonString + "出现错误请重试");
}
var myuser = new user { WxOpenId = jsonOAuthorObj.openid }.SelectObject();
//注册成功后直接登录，授权会判断是否有账户
if (myuser == null)
{
//拉取用户信息(需scope为 snsapi_userinfo)，和unionid(只有在用户将公众号绑定到微信开放平台帐号后，才会出现该字段)
jsonString = await (await webClient.GetAsync("https://api.weixin.qq.com/sns/userinfo?access_token=" + jsonOAuthorObj.access_token + "&openid=" + jsonOAuthorObj.openid + "&lang=zh_CN")).Content.ReadAsStringAsync();
dynamic jsonObj = JsonConvert.DeserializeObject(jsonString, new { nickname = "", headimgurl = "", sex = "", openid = "", country = "", province = "", city = "",unionid=""}.GetType());
//查询系统中是否存在unionid用户信息，若存在则更新当前用户openid，并直接登录，如果不存在的话则需要创建一个新的用户信息
var isExistUserInfo=new user(){unionid=unionid }.SelectObject();
if(isExistUserInfo!=null)//存在该用户记录
{
//更新公众号openid
 isExistUserInfo.WxOpenId=jsonObj.openid;
 isExistUserInfo.Update();
//存在用户信息直接登录
return Redirect(url);
}
else//不存在该用户记录
{
//创建用户
int cUserId = new user { Wximage= jsonObj.headimgurl, WxNickName = jsonObj.nickname, WxOpenId = jsonObj.openid, Sex = Convert.ToInt32(jsonObj.sex), Country = jsonObj.country, Province = jsonObj.province, City = jsonObj.city，unionid=unionid }.Create();
return RedirectToAction("WxRegister", "Login", new { ReturnUrl = url });
}
}
else
{
//存在用户信息直接登录
return Redirect(url);
}
}
catch (Exception e)
{
return View("MessageInfo", "", e.ToString());
}
}