Bucket POST must contain a field named 'AWSAccessKeyId' with SigV4-CodePudding

I am trying to do a simple create_presigned_post using python and boto3.

import boto3
from botocore.config import Config

def s3_upload_creds():
    REGION = 'eu-west-2'
    s3 = boto3.client('s3', 
    aws_access_key_id=aws_access_key_id,
    aws_secret_access_key=aws_secret_access_key, region_name=REGION, config=Config(signature_version='s3v4'))

    return s3.generate_presigned_post(
        Bucket = bucket,
        Key = key,
        ExpiresIn=3600
    )

upload_fields = s3_upload_creds()

url = upload_fields['url']
upload_fields = upload_fields['fields']

"""<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
  </head>
  <body>
    <form action="{url}" method="post" enctype="multipart/form-data">
          <input type="text" id="x-amz-algorithm" name="x-amz-algorithm" value="AWS4-HMAC-SHA256" /><br />
          <input type="text" id="x-amz-credential" name="x-amz-credential" value="{creds}" /><br />
          <input type="text" id="x-amz-date" name="x-amz-date" value="{date}" /><br />
          <input type="text" id="x-amz-policy" name="policy" value="{policy}" /><br />
          <input type="text" id="signature" name="signature" value="{signature}" />
          <input type="text" id="key" name="key" value="{key}" />

          File:
          <input type="file"   name="file" /> <br />
    <input type="submit" name="submit" value="Upload to Amazon S3" />
  </form>
</html>""".format(
  url=url,
  creds=upload_fields['x-amz-credential'],
  date=upload_fields['x-amz-date'],
  policy=upload_fields['policy'],
  signature=upload_fields['x-amz-signature'],
  key=upload_fields['key']
)

However I receive this error.

<?xml version="1.0" encoding="UTF-8"?>
<Error>
    <Code>InvalidArgument</Code>
    <Message>Bucket POST must contain a field named 'AWSAccessKeyId'.  If it is specified, please check the order of the fields.</Message>
    <ArgumentName>AWSAccessKeyId</ArgumentName>
    <ArgumentValue></ArgumentValue>
    <RequestId>DFEDBZFEES4PFQV3</RequestId>
    <HostId>k7wj2Ehd/DjtpVk OtG0qGFRECtTYkQv64hEwLRFkqKR4Qfhj0nbOHKS5DNqWo/TTGR3BbC6k=</HostId>
</Error>

Browsing solutions online I found that if the file is specified before the other fields, it will not work. I have verified that it is not the case on my browser and Postman.

I tried to add the field but it gives me this error.

<?xml version="1.0" encoding="UTF-8"?>
<Error>
    <Code>InvalidRequest</Code>
    <Message>The authorization mechanism you have provided is not supported. Please use AWS4-HMAC-SHA256.</Message>
    <RequestId>AYGPAQPQFDWFE3Q6N</RequestId>
    <HostId>aYTEn/SyElUsyFPRFEDWtZ8SYKuQWB7bvaxvmq0tvXkPFDWlYAixsO6ue tEbVstaWGRF4KY=</HostId>
</Error>

I do not understand why aws needs AWSAccessKeyId since I can see it at the start of x-amz-credential: AK-----------------R/date/region/s3/aws4_requests

I Have looked at theses: Link Link

CodePudding user response：

Thanks Anon Coward for your help.

The issue come from the html form I used. One of the fields where rename with the name html attribute wrongly, causing and error which message is out of context. The sample above should change name='signature' to name='x-amz-signature'.

Note that the field names returned from create_presigned_post are:

key
x-amz-algorithm
x-amz-credential
x-amz-date
policy
x-amz-signature