used by 'Lessons learned from handling JWT on mobile' article on Medium

base64_decoding_function.swift

func base64String(_ input: String) -> String {
    var base64 = input
        .replacingOccurrences(of: "-", with: "+")
        .replacingOccurrences(of: "_", with: "/")

    switch base64.count % 4 {
    case 2:
        base64 = base64.appending("==")

    case 3:
        base64 = base64.appending("=")

    default:
        break
    }

    return base64
}