String+URLSafe.swift

import Foundation

/// Adds a utility method for decoding base64url-encoded data, like ID tokens.
public extension String {

    /// Decodes base64url-encoded data.
    func a0_decodeBase64URLSafe() -> Data? {
        let lengthMultiple = 4
        let paddingLength = lengthMultiple - count % lengthMultiple
        let padding = (paddingLength < lengthMultiple) ? String(repeating: "=", count: paddingLength) : ""
        let base64EncodedString = self
            .replacingOccurrences(of: "-", with: "+")
            .replacingOccurrences(of: "_", with: "/")
            + padding
        return Data(base64Encoded: base64EncodedString)
    }

}