// an important problem for ListBuckets() getting signed with
	// different regions.
	if region == "" {
		region = sRegion
	}
	// Should validate region, only if region is set.
	if !isValidRegion(sRegion, region) {
		return ch, ErrAuthorizationHeaderMalformed
	}
	if credElements[2] != string(stype) {
		if stype == serviceSTS {
			return ch, ErrInvalidServiceSTS
		}
		return ch, ErrInvalidServiceS3