我尝试使用JWT的developerToken尝试获取Apple Music SDK的userToken失败。我已经使用了pelauimagineering / apple-music-token-generator，我可以得到一个有效且静态的userToken。但苹果建议动态，所以我试图再次使用JWT。
有人可以告诉我，我的代码有什么问题吗？谢谢
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)
}