内容类型限制为pdf文件无法在基于浏览器的上传到s3

Question

内容类型限制在亚马逊s3政策中不起作用： 使用此策略，我可以上传任何文件类型，我必须仅限制pdf文件

以下是我的代码：

    $bucket = 'test'; // the name you've chosen for the bucket
    $key = 'upload/${filename}'; 
    $success_action_redirect = 'localhost/test.html'; 
    $content_type = 'application/pdf';
    $acl = 'private'; 

   $policy = '
     { "expiration": "2016-08-23T12:00:00.000Z",
       "conditions": [
          {"bucket": "'.$bucket.'"},
          ["starts-with", "$key", ""],
          {"acl": "'.$acl.'"},
          {"success_action_redirect": "'.$success_action_redirect.'"},
          ["starts-with", "$Content-Type", "'.$content_type.'"],
          {"x-amz-meta-uuid": "14365123651274"},
          ["starts-with", "$x-amz-meta-tag", ""],
          ["content-length-range", 0, 10485760]
       ]
    }';

    <form action="bucketUrl" method="post" enctype="multipart/form-data" 
     id="s3-post">
    <input type="hidden" name="key" value="<?php echo $key; ?>">
    <input type="hidden" name="acl" value="<?php echo $acl; ?>">
    <input type="hidden" name="success_action_redirect" value="<?php echo $success_action_redirect; ?>">
    <input type="hidden" name="Content-Type" value="<?php echo $content_type; ?>">
    <input type="hidden" name="x-amz-meta-uuid" value="14365123651274">
    <input type="hidden" name="x-amz-meta-tag" value="">
    <input type="hidden" name="AWSAccessKeyId" value="<?php echo $aws_access_key; ?>">
    <input type="hidden" name="Policy" value="<?php echo base64_encode($policy); ?>">
    <input type="hidden" name="Signature" value="<?php echo base64_encode(hash_hmac('sha1', base64_encode($policy), $aws_secret_key, true)); ?>">
    <input type="file" name="file" class="input_file">
    <input type="submit" name="submit" class="s3_upload" value="Upload to Amazon S3">