Post policy

Policy、Signature Building Methods

Policy Building Methods

Description

Policy is a JSON document encoded with UTF-8 and Base64, which specifies the conditions that the request must meet and is used to authenticate the content. Depending on how you design policy documents, you can use them for each upload, for each user, for all uploads, or for other designs that meet your needs.
Policy document example

{    
    "expiration": "2015-01-01T12:00:00.000Z",
     "conditions": [
        ["eq","$acl", "public-read" ],
        ["eq","$bucket", "mybucket" ],
        ["starts-with", "$key", "2015/01/"]
    ]
}

Expiration

The expiration element uses the ISO 8601 UTC date format to specify the expiration date of the policy, that is, it can only be uploaded before the specified time. Uploads after this time will be considered illegal, and KS3 will return 403. Note: the time zone is Green time (zero time zone) instead of Beijing time (East 8 zone)

Conditions

The validation conditions for the uploaded content in the Policy document. Each form field you specify in the form (except KSSAccessKeyId、Signature、file、policy and bucket must be included in the condition list.

Note: all variables in the form are extended before the Policy is validated. Therefore, all condition matches should be performed for the extended fields. For example, if you set the key field to 2015/01/${filename}, the condition in your policy might be [ "starts-with", "$key", "2015/01/" ]。Do not enter. [ "starts-with", "$key", "2015/01/${filename}" ]

Condition Matching Rule

Character Escape

The characters in the following table must be converted in the Policy document

Signature Building Methods

For authenticated Post requests, the HTML form must contain Policy and Signature information. Policy controls which values are allowed in the request.
The specific process of calculating Signature is as follows:
1) Create a UTF-8 encoded Policy document. See the Policy building method for details.
2) Base64 code the policy, whose value is the value that the policy form field should fill in, and use the value as the String To Sign.
3）Signature = Base64(HMAC-SHA1(YourSecretKey, UTF-8-Encoding-Of(StringToSign ) ) );