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V4 Browser-based Authorized POST Request

OBS supports browser-based POST object uploading requests. The authentication information about these requests is uploaded by a form. Table 1 lists the mandatory parameters.

Table 1 V4 POST uploading authentication parameters in the form

Parameter	Description
Policy	The value of this parameter is a code in Base64 format. It is the code of the security policy of this request.
x-amz-algorithm	Indicates a signature algorithm. For a V4 signature, the value of the parameter is fixed to AWS4-HMAC-SHA256.
x-amz-credential	In addition to the access key ID, region and service information must be provided. The information must be the same as that used to calculate the Signing Key. The value of this parameter is expressed in the following format: <your-access-key-id>/<date>/<AWS-region>/<AWS-service>/aws4_request.OBS region The value is the same as that used for common authentication. Example: AKIAIOSFODNN7EXAMPLE/20150721/region-1/s3/aws4_request.
x-amz-date	Indicates the request generation time. It is in the ISO 8601 format. The value must be the same as that of the x-am-date field in the policy. Example: 20150721T201207Z.
x-amz-signature	Indicates the HMAC-SHA256 hash value of the policy in V4.

Policy is a character string in JSON format and consists of two parts:

• expiration (indicates the request expiration time).
• conditions (indicates parameter restrictions in the form).

An example is as follows:

{ 
 "expiration": "2015-08-06T12:00:00.000Z", 
 "conditions": [ 
   {"bucket": "bucketname"}, 
   ["starts-with", "$key", "user/user1/"], 
   {"acl": "public-read"}, 
   {"success_action_redirect": 
"http://acl6.obs.example.com/successful_upload.html"}, 
   ["starts-with", "$Content-Type", "image/"], 
   {"x-amz-meta-uuid": "14365123651274"}, 
   ["starts-with", "$x-amz-meta-tag", ""], 
   {"x-amz-credential": "AKIAIOSFODNN7EXAMPLE/20150806/region-1/s3/aws4_request"}, 
   {"x-amz-algorithm": "AWS4-HMAC-SHA256"}, 
   {"x-amz-date": "20150806T000000Z" } 
 ] 
 }

Table 2 lists the mandatory parameters of Policy.

Table 2 Mandatory parameters of Policy in V4 POST uploading requests

Parameter	Description
x-amz-algorithm	Indicates the used signature algorithm. In V4, the value of the parameter is AWS4-HMAC-SHA256.
x-amz-credential	In addition to the access key ID, region and service information must be provided. The information must be the same as that used to calculate the Signing Key. The value of this parameter is expressed in the following format: <your-access-key-id>/<date>/<AWS-region>/<AWS-service>/aws4_request. Example: AKIAIOSFODNN7EXAMPLE/20150721/region-1/s3/aws4_request.
x-amz-date	Indicates the Start time of the validity period of Signing Key. The value is expressed in ISO 8601 format. The value must be the same as that of the x-am-date field in the Signing Key. Example: 20150721T201207Z

The signature calculation process of V4 POST uploading requests is similar to that of V4 common requests. The only difference lies in the Policy in the request used by StringToSign in V4. The Policy is obtained by Base64 encoding based on the original Policy character string. Figure 1 shows the computing process.

Figure 1 Signature calculation process of objects uploaded using V4 POST uploading requests

Parent topic: Authenticating a Request