func getSignature(signingKey []byte, stringToSign string) string {
	return hex.EncodeToString(sumHMAC(signingKey, []byte(stringToSign)))
}

// Check to see if Policy is signed correctly.
func doesPolicySignatureMatch(formValues http.Header) (auth.Credentials, APIErrorCode) {
	// For SignV2 - Signature field will be valid
	if _, ok := formValues[xhttp.AmzSignatureV2]; ok {
		return doesPolicySignatureV2Match(formValues)
	}

				},
				"Policy": []string{"policy"},
			},
			expected: ErrNone,
		},
	}

	// Run each test case individually.
	for i, testCase := range testCases {
		_, code := doesPolicySignatureMatch(testCase.form)
		if code != testCase.expected {
			t.Errorf("(%d) expected to get %s, instead got %s", i, niceError(testCase.expected), niceError(code))
		}
	}
}