base64處理

extension Data {
    // Encode `self` with URL escaping considered.
    var base64URLEncoded: String {
        let base64Encoded = base64EncodedString()
        return base64Encoded
            .replacingOccurrences(of: "+", with: "-")
            .replacingOccurrences(of: "/", with: "_")
            .replacingOccurrences(of: "=", with: "")
    }
}

extension String {
    // Returns the data of `self` (which is a base64 string), with URL related characters decoded.
    var base64URLDecoded: Data? {
        let paddingLength = 4 - count % 4
        // Filling = for %4 padding.
        let padding = (paddingLength < 4) ? String(repeating: "=", count: paddingLength) : ""
        let base64EncodedString = self
            .replacingOccurrences(of: "-", with: "+")
            .replacingOccurrences(of: "_", with: "/")
            + padding
        return Data(base64Encoded: base64EncodedString)
    }
}