Couchbase CE has many fewer roles than EE. If you try to create an index as an unauthenticated user, e.g.,

curl [http://localhost:9093/query/service] -d 'statement=create primary index on default;'

The error message that comes back is:

[{"code":13014,"msg":"User does not have credentials to run index operations. Add role query_manage_index on default to allow the query to run."}]

Yet the CE version doesn't have a query_manage_index role. The query does work you supply user credentials with the Administrator role, or with the "Bucket Full Access" role.