我指的是 AWS Mobile Hub 开发人员指南（用于集成基于电子邮件的用户登录）http://docs.aws.amazon.com/mobile-hub/latest/developerguide/amhd-dg.pdf
标题为：为 AWS 移动服务 (Android - Java) 设置您的应用程序的主题
最后一步第 8 步结果应该是“IdentityManager：得到用户 ID：us-east-1:abcabcabc-0be6-444e-b101-abcabcabc”，但我得到“D/IdentityManager：得到用户 ID：null”
异常的堆栈跟踪：
E/IdentityManager: Unauthenticated access is not supported for this identity pool. (Service: AmazonCognitoIdentity; Status Code: 400; Error Code: NotAuthorizedException; Request ID: d275fc19-b700-11e7-bac5-5d9ca7c93439)
com.amazonaws.services.cognitoidentity.model.NotAuthorizedException: Unauthenticated access is not supported for this identity pool. (Service: AmazonCognitoIdentity; Status Code: 400; Error Code: NotAuthorizedException; Request ID: d275fc19-b700-11e7-bac5-5d9ca7c93439)
at com.amazonaws.http.AmazonHttpClient.handleErrorResponse(AmazonHttpClient.java:729)
at com.amazonaws.http.AmazonHttpClient.executeHelper(AmazonHttpClient.java:405)
at com.amazonaws.http.AmazonHttpClient.execute(AmazonHttpClient.java:212)
at com.amazonaws.services.cognitoidentity.AmazonCognitoIdentityClient.invoke(AmazonCognitoIdentityClient.java:559)
at com.amazonaws.services.cognitoidentity.AmazonCognitoIdentityClient.getId(AmazonCognitoIdentityClient.java:445)
at com.amazonaws.auth.AWSAbstractCognitoIdentityProvider.getIdentityId(AWSAbstractCognitoIdentityProvider.java:172)
at com.amazonaws.auth.CognitoCredentialsProvider.getIdentityId(CognitoCredentialsProvider.java:402)
at com.amazonaws.auth.CognitoCachingCredentialsProvider.getIdentityId(CognitoCachingCredentialsProvider.java:465)
at com.amazonaws.mobile.auth.core.IdentityManager$1.run(IdentityManager.java:334)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:422)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
------------------------
D/IdentityManager: Got user ID: null