微信小程序实现微信登陆（TP5后端）

思路：

小程序登录获取code，将code传到后台；
后台用code得到微信用户id，即openid，将openid存储在用户表中，完成绑定
登录时，再次获取code并传给后台，得到openid，若用户表中存在，便可直接登录

以下仅是代码片段，更多代码在Github

back_end/application/api/controller
mini_program/pages/student_mine
mini_program/pages/login

微信与小程序账号绑定

小程序前端获取code，将code与id传回后台

wx_binding: function () {
    var that = this
    wx.login({
        success: function (res) {
            console.log("code: ", res.code)
            wx.request({
                url: \'******/user/wxbinding\',
                data: {
                    code: res.code,
                    id: getApp().globalData.user.id,
                },
                method: "POST",
                header: {
                    "Content-Type": "application/x-www-form-urlencoded"
                },
            })
        }
    })
}

ThinkPHP5后端接受到code，用code得到openid，并将openid与账号id绑定

public function wxBinding() {
    $url = "https://api.weixin.qq.com/sns/jscode2session";
    // 参数
    $params = array();
    $params[\'appid\'] = \'******\';
    $params[\'secret\'] = \'******\';
    $params[\'js_code\'] = $_POST[\'code\'];
    $params[\'grant_type\'] = \'authorization_code\';

    // 微信API返回的session_key 和 openid
    $arr = $this -> httpCurl($url, $params, \'POST\');
    $arr = json_decode($arr, true);

    // 判断是否成功
    if (isset($arr[\'errcode\']) && !empty($arr[\'errcode\'])) {
        return json([\'error_code\' => \'2\', \'msg\' => $arr[\'errmsg\'], "result" => null]);
    }
    $openid = $arr[\'openid\'];

    // 插入openid
    $bind = db(\'user\') -> where(\'id\', $_POST[\'id\']) -> update([\'openid\' => $openid]);
    if ($bind) {
        return json([\'error_code\' => \'0\', \'msg\' => \'绑定成功\']);
    } else {
        // 找不到账号
        return json([\'error_code\' => \'1\', \'msg\' => \'绑定失败\']);
    }
}

解密获取openid

use \think\Exception;

function httpCurl($url, $params, $method = \'GET\', $header = array(), $multi = false) {
    date_default_timezone_set(\'PRC\');
    $opts = array(
        CURLOPT_TIMEOUT => 30,
        CURLOPT_RETURNTRANSFER => 1,
        CURLOPT_SSL_VERIFYPEER => false,
        CURLOPT_SSL_VERIFYHOST => false,
        CURLOPT_HTTPHEADER => $header,
        CURLOPT_COOKIESESSION => true,
        CURLOPT_FOLLOWLOCATION => 1,
        CURLOPT_COOKIE
            => session_name(). \'=\'.session_id(),
    );

    /* 根据请求类型设置特定参数 */
    switch (strtoupper($method)) {
        case \'GET\':
            // $opts[CURLOPT_URL] = $url . \'?\' . http_build_query($params);
            // 链接后拼接参数  &  非？
            $opts[CURLOPT_URL] = $url. \'?\'.http_build_query($params);
            break;
        case \'POST\':                //判断是否传输文件
            $params = $multi ? $params : http_build_query($params);
            $opts[CURLOPT_URL] = $url;
            $opts[CURLOPT_POST] = 1;
            $opts[CURLOPT_POSTFIELDS] = $params;
            break;
        default:
            throw new Exception(\'不支持的请求方式！\');
    }

    /* 初始化并执行curl请求 */
    $ch = curl_init();
    curl_setopt_array($ch, $opts);
    $data = curl_exec($ch);
    $error = curl_error($ch);
    curl_close($ch);
    if ($error) throw new Exception(\'请求发生错误：\'.$error);
    return $data;
}

微信登录小程序

小程序前端返回code

wx.login({
    success: function (res) {
        console.log("code: ", res.code)
        wx.request({
            url: \'******/user/wxlogin\',
            data: {
                code: res.code,
            },
            method: "POST",
            header: {
                "Content-Type": "application/x-www-form-urlencoded"
            },
            success: function (res) {
            },
        })
    }
})

后端获取openid，若有用户，返回用户信息给小程序

public function wxLogin() {
    if (empty($_POST[\'code\'])) {
        return json([\'error_code\' => \'1\', \'msg\' => \'请输入code！\']);
    }
    $url = "https://api.weixin.qq.com/sns/jscode2session";
    // 参数
    $params = array();
    $params[\'appid\'] = \'******\';
    $params[\'secret\'] = \'******\';
    $params[\'js_code\'] = $_POST[\'code\'];
    $params[\'grant_type\'] = \'authorization_code\';

    // 微信API返回的session_key 和 openid
    $arr = $this -> httpCurl($url, $params, \'POST\');
    $arr = json_decode($arr, true);

    // 判断是否成功
    if (isset($arr[\'errcode\']) && !empty($arr[\'errcode\'])) {
        return json([\'error_code\' => \'2\', \'msg\' => $arr[\'errmsg\'], "result" => null]);
    }

    $openid = $arr[\'openid\'];
    // $session_key = $arr[\'session_key\'];

    // 从数据库中查找是否有该openid
    $user = db(\'user\') -> where(\'openid\', $openid) -> find();

    if ($user) {
        unset($user[\'openid\']);  // 删除openid
        unset($user[\'password\']);  // 删除密码
        return json([\'error_code\' => \'0\', \'msg\' => \'登录成功\', \'data\' => $user]);

    } else {
        // 该微信用户没有绑定账号
        return json([\'error_code\' => \'1\', \'msg\' => \'您没有绑定账号，请登录后在“我的”页面绑定~\']);
    }
}

学习博客：
小程序和ThinkPHP5结合实现登录状态（附代码）
微信小程序授权登录+Tp5后端
 从零开始开发微信小程序（三）：微信小程序绑定系统账号并授权登录之微信端