class Aws::S3::PresignedPost

def signature_fields(datetime)
  fields = {}
  fields['x-amz-credential'] = credential_scope(datetime)
  fields['x-amz-algorithm'] = 'AWS4-HMAC-SHA256'
  fields['x-amz-date'] = datetime
  if session_token = @credentials.session_token
    fields['x-amz-security-token'] = session_token
  end
  fields
end