使用Amazon Cognito开发者身份

我正在关注亚马逊文档,但它不像宣传的那样工作.我也有最新的sdk.self.identity =下面的代码不起作用,因为它是只读的.

@implementation DeveloperAuthenticatedIdentityProvider
/*
 * Use the token method to communicate with your backend to get an
 * identityId and token.
 */

- (AWSTask ) token {
    //Write code to call your backend:
    //Pass username/password to backend or some sort of token to authenticate user
    //If successful, from backend call getOpenIdTokenForDeveloperIdentity with logins map 
    //containing "your.provider.name":"enduser.username"
    //Return the identity id and token to client
    //You can use AWSTaskCompletionSource to do this asynchronously

    // Set the identity id and return the token
    self.identityId = response.identityId;
    return [AWSTask taskWithResult:response.token];
}

@end

我该如何纠正这个？谢谢.