Generate random string with custom length

RandomString.swift

extension String {
 static func random(_ length: Int = 20) -> String {
        let base = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
        var randomString: String = ""

        for _ in 0..<length {
            let randomValue = arc4random_uniform(UInt32(base.characters.count))
            randomString += "\(base[base.characters.index(base.startIndex, offsetBy: Int(randomValue))])"
        }

        return randomString
    }

}