Create a Pre-signed URL for Google Storage in Swift using Vapor

GoogleCloud.swift

import Foundation
import Vapor
import Core
import VaporJWT

class GoogleCloud {
    func generatePreSignedURL() -> String? {
        let accessId = "project@project-xxxxx.iam.gserviceaccount.com"

        let bucketName = "bucketname"
        let expiry = (1000*60) + Int(Date().timeIntervalSince1970)
        let key = "file.txt"
        let policyString = "GET\n\n\n\(expiry)\n/\(bucketName)/\(key)"
        let policyData = policyString.data(using: .utf8)!

        do {
            let privateKey = try DataFile().load(path: "private.der")
            let signer = RS256(key: privateKey)
            let policyBytes = [UInt8](policyData)
            let signatureBytes = try signer.sign(policyBytes)

            let rfc3986Reserved = NSCharacterSet(charactersIn:"!*'();:@&=+$,/?#[]")
            let escapedSignatureString = signatureBytes.base64String.addingPercentEncoding(withAllowedCharacters: rfc3986Reserved.inverted)!

            let signedUrlString = "https://storage.googleapis.com/\(bucketName)/\(key)?GoogleAccessId=\(accessId)&Expires=\(expiry)&Signature=\(escapedSignatureString)"
            return signedUrlString
        } catch {
            print(error.localizedDescription)
            return nil
        }
    }
}