get_email_with_apple_auth_code.cs

private async Task<string> GetEmailFromAppleCode(string appleCode)
{
  string privateKey = System.IO.File.ReadAllText(Path.Combine(this.environment.ContentRootPath, "AuthKey_XXXXXXXXXX.p8"));
  AppleAuthProvider provider = new AppleAuthProvider(
    "com.your.app",
    "XXXXXXXXXX",
    "XXXXXXXXXX",
    "https://auth.yourapp.com/callback", // I don't know why it must be here but it is not used
    string.Empty
  );

  AuthorizationToken authorizationToken = await provider.GetAuthorizationToken(appleCode, privateKey);
  JwtSecurityToken jwt = new JwtSecurityToken(authorizationToken.Token);

  return jwt.Claims.First(c => c.Type == ClaimTypes.Email).Value;
}