Amazon.S3.Util.S3PostUploadSignedPolicy.GetSignedPolicyFromJson C# (CSharp) Method

        public static S3PostUploadSignedPolicy GetSignedPolicyFromJson(string policyJson)
        {
            JsonData json;
            try { json = JsonMapper.ToObject(policyJson); }
            catch (Exception e)
            {
                throw new ArgumentException("Invalid JSON document", e);
            }

            if (null == json[KEY_POLICY] || !json[KEY_POLICY].IsString)
                throw new ArgumentException(string.Format(CultureInfo.InvariantCulture, "JSON document requires '{0}' field"), KEY_POLICY);
            if (null == json[KEY_SIGNATURE] || !json[KEY_SIGNATURE].IsString)
                throw new ArgumentException(string.Format(CultureInfo.InvariantCulture, "JSON document requires '{0}' field"), KEY_SIGNATURE);
            if (null == json[KEY_ACCESSKEY] || !json[KEY_ACCESSKEY].IsString)
                throw new ArgumentException(string.Format(CultureInfo.InvariantCulture, "JSON document requires '{0}' field"), KEY_ACCESSKEY);

            return new S3PostUploadSignedPolicy
            {
                Policy = json[KEY_POLICY].ToString(),
                Signature = json[KEY_SIGNATURE].ToString(),
                AccessKeyId = json[KEY_ACCESSKEY].ToString()
            };
        }