问使用JWT获取Apple Music SDK的userToken时出错

EN

func fetchDeveloperToken() -> String? {
   func fetchDeveloperToken() -> String? {
    let iat = Date().timeIntervalSince1970
    let days = TimeInterval(24*60*60*120) //120 days
    let exp = TimeInterval(iat + days)
    let kid = "TBESJXXXXX"
    let iss = "KQ6Z6XXXXX"
    let alg = "ES256"
    let secret = "MIGTAgEAMBMGByqEU7ZHQsoVfmKCCxS5W6BnCgCgYIKoZIzj0AAQcggNoN7dTkNG/8timkkf+Z2toogAqN41YgOXXXXXXXXXXXXXXXXXXsecretkey"
    let header:[AnyHashable:Any] = ["alg":alg, "kid":kid]
    let payload:[AnyHashable:Any] = ["iss": iss,
                                     "iat": iat,
                                     "exp": exp]
    let algorithm256 = JWTAlgorithmHS256()
    return JWT.encodePayload(payload, withSecret: secret, withHeaders: header, algorithm: algorithm256)
}