if credElements[2] != string(stype) {
		if stype == serviceSTS {
			return ch, ErrInvalidServiceSTS
		}
		return ch, ErrInvalidServiceS3
	}
	cred.scope.service = credElements[2]
	if credElements[3] != "aws4_request" {
		return ch, ErrInvalidRequestVersion
	}
	cred.scope.request = credElements[3]
	return cred, ErrNone
}

// Parse signature from signature tag.