<?php

function gmt_iso8601($time) {

    $dtStr = date("c", $time);

    $mydatetime = new DateTime($dtStr);

    $expiration = $mydatetime->format(DateTime::ISO8601);

    $pos = strpos($expiration, '+');

    $expiration = substr($expiration, 0, $pos);

    return $expiration."Z";

}

//阿里云官方提供的秘钥

$id= '6MKOqxGiGU4AUk44';

$key= 'ufu7nS8kS59awNihtjSonMETLI0KLy';

$host = 'http://post-test.oss-cn-hangzhou.aliyuncs.com';

$now = time();

$expire = 30; //设置该policy超时时间是10s. 即这个policy过了这个有效时间，将不能访问

$end = $now + $expire;

$expiration = gmt_iso8601($end);

$dir = 'user-dir/';

//最大文件大小.用户可以自己设置

$condition = array(0=>'content-length-range', 1=>0, 2=>1048576000);

$conditions[] = $condition;

//表示用户上传的数据,必须是以$dir开始, 不然上传会失败,这一步不是必须项,只是为了安全起见,防止用户通过policy上传到别人的目录

$start = array(0=>'starts-with', 1=>'$key', 2=>$dir);

$conditions[] = $start;

$arr = array('expiration'=>$expiration,'conditions'=>$conditions);

$policy = json_encode($arr);

$base64_policy = base64_encode($policy);

$string_to_sign = $base64_policy;

$signature = base64_encode(hash_hmac('sha1', $string_to_sign, $key, true));

$response = array();

$response['accessid'] = $id;

$response['host'] = $host;

$response['policy'] = $base64_policy;

$response['signature'] = $signature;

$response['expire'] = $end;

//这个参数是设置用户上传指定的前缀

$response['dir'] = $dir;

$response['code']=1;

echo json_encode(['data'=>$response,'status'=>1]);

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <title></title>

    <script type="text/javascript" src="http://apps.bdimg.com/libs/jquery/2.1.4/jquery.min.js"></script>

</head>

<body>

<div>

    <input type="hidden"  > <img src="" style="width: 200px;height: 100px; display: none">

    <input type="file" name="upfile" accept="image/*" >

</div>

<script type="text/javascript">

    var expire =0;

     sign_obj='';

    var serverUrl='auth.php';

    $(function () {

        $("div").on("change",'input[type="file"]',function(evt){

            $this=$(this);

            var files = evt.target.files;

            var file=files[0];

            if(file.size > 10*1024*1024 ){

                alert('too big');

                return false;

            }

            get_signature();

            if(sign_obj == '') {

                alert(sign_obj);

               alert('签名error,请重试');

                return false;

            }

            var g_object_name=sign_obj.dir+random_string()+get_suffix(file.name);

            var request = new FormData();

            request.append("OSSAccessKeyId",sign_obj.accessid);//Bucket 拥有者的Access Key Id。

            request.append("policy",sign_obj.policy);//policy规定了请求的表单域的合法性

            request.append("Signature",sign_obj.signature);//根据Access Key Secret和policy计算的签名信息，OSS验证该签名信息从而验证该Post请求的合法性

            request.append("key",g_object_name);//文件名字，可设置路径

            request.append("success_action_status",'200');// 让服务端返回200,不然，默认会返回204

            request.append('x-oss-object-acl', 'public-read');

            request.append('file', file);

            $.ajax({

                url : sign_obj.host,  //上传阿里地址

                data : request,

                processData: false,//默认true，设置为 false，不需要进行序列化处理

                cache: false,//设置为false将不会从浏览器缓存中加载请求信息

                async: false,//发送同步请求

                contentType: false,//避免服务器不能正常解析文件---------具体的可以查下这些参数的含义

                dataType: 'xml',//不涉及跨域  写json即可

                type : 'post',

                success : function(callbackHost, request) {     //callbackHost：success,request中就是 回调的一些信息，包括状态码什么的

                    var origin=sign_obj.host+'/'+g_object_name;

                    var src=origin;

                    $this.closest('div').find('img').attr('src', src).show();

                    $this.closest('div').find('.imgclose').show();

                },

                error : function(returndata) {

                    console.log("return data:"+returndata);

                    alert('上传图片出错啦,请重试')

                }

            });

        });

    })

    function random_string(len) {

        len = len || 32;

        var chars = 'ABCDEFGHJKMNPQRSTWXYZabcdefhijkmnprstwxyz2345678';

        var maxPos = chars.length;

        var pwd = '';

        for (i = 0; i < len; i++) {

            pwd += chars.charAt(Math.floor(Math.random() * maxPos));

        }

        return pwd;

    }

    function get_suffix(filename) {

        var pos = filename.lastIndexOf('.')

        var suffix = ''

        if (pos != -1) {

            suffix = filename.substring(pos)

        }

        return suffix;

    }

    //获取签名信息

    function send_request()

    {

        var xmlhttp = null;

        if (window.XMLHttpRequest)

        {

            xmlhttp=new XMLHttpRequest();

        }

        else if (window.ActiveXObject)

        {

            xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");

        }

        if (xmlhttp!=null)

        {

            xmlhttp.open( "GET", serverUrl, false );

            xmlhttp.send( null );

            return xmlhttp.responseText

        }

        else

        {

            alert("Your browser does not support XMLHTTP.");

        }

    }

    function get_signature()

    {

        //可以判断当前expire是否超过了当前时间,如果超过了当前时间,就重新取一下.3s 做为缓冲

        now = timestamp = Date.parse(new Date()) / 1000;

        if (expire < now + 3)

        {

            var body = send_request();

            var obj =JSON.parse(body);

            if(obj.status ==1  && obj.data.code == 1){

                sign_obj= obj.data;

                expire= parseInt(sign_obj['expire']);

                return true;

            }

            return true;

        }

        return false;

    };

</script>

</body>

</html>