// Do the same for the headers.
		for key, value := range testCase.headers {
			req.Header.Set(key, value)
		}

		// parse form.
		req.ParseForm()

		// Check if it matches!
		err := doesPresignedSignatureMatch(payloadSHA256, req, testCase.region, serviceS3)
		if err != testCase.expected {
			t.Errorf("(%d) expected to get %s, instead got %s", i, niceError(testCase.expected), niceError(err))
		}
	}

	sha256sum := getContentSha256Cksum(r, stype)
	switch {
	case isRequestSignatureV4(r):
		return doesSignatureMatch(sha256sum, r, region, stype)
	case isRequestPresignedSignatureV4(r):
		return doesPresignedSignatureMatch(sha256sum, r, region, stype)
	default:
		return ErrAccessDenied
	}
}

// Verify if request has valid AWS Signature Version '4'.