SASL-AUTH SCRAM-SHA512 fails just for the Administrator user

Background
This is a follow on from JVMCBC-528

Problem

When trying to authenticate as "Administrator" user using SCRAM-SHA512 the following error is reported in the memcached.log:

2018-04-17T15:42:25.664194+01:00 NOTICE 47: HELO [{"a":"couchbase-java-client/2.5.7 (git: 2.5.6-7-g17b4f94, core: 1.5.6-3-gca2bb88) (Mac OS X/10.13.4 x86_64; Java HotSpot(TM) 64-Bit Server VM 1.8.0_92-b14)","i":"2B291CEDFD320B27/FFFFFFFF809C4A4E"}] TCP NODELAY, XATTR, Select Bucket, XERROR [ 127.0.0.1:50183 - 127.0.0.1:11210 (not authenticated) ]

2018-04-17T15:42:25.827595+01:00 WARNING 47: StartSaslAuthTask::execute(): UUID:[2aa6d411-b5b8-4eb8-7141-30bb8083cbe7] An exception occurred: cb::cbsasl::User::getPassword: requested mechanism not available

This error message is also passed back to the client in the following format

{{"error":{"context":"An exception occurred","ref":"2aa6d411-b5b8-4eb8-7141-30bb8083cbe7"}}

When any of the other users are used, it authenticates successfully.

Steps to reproduce

• Couchbase 5.0.0 on MacOS
• Java SDK 2.5.7

1. Setup a single bucket
2. Run the following code:

   import com.couchbase.client.java.Bucket;

   import com.couchbase.client.java.Cluster;

   import com.couchbase.client.java.CouchbaseCluster;

   public class GetTTL

   {

   public static void main(String [] args)

   {

   Cluster cluster = CouchbaseCluster.create("localhost");

   System.out.println("Authenticating as administrator");

   cluster.authenticate("Administrator", "password");

   // Open the test bucket.

   System.out.println("Opening the bucket test");

   Bucket test = cluster.openBucket("test");

   }

   }

Request

• What is cause the failure?
• Should the Server be passing the exception error back to the client
  • If it should is it in the correct format?