    public const string XCaSignature = "x-ca-signature";
    public const string XCaSignatureMethod = "x-ca-signature-method";
    public const string XCaSignatureHeaders = "X-Ca-Signature-Headers";
    public const string ContentMD5 = "Content-MD5";
    public const string ContentType = "Content-Type";
    public const string Date = "Date";
    public const string Accept = "Accept";
}