title: MongoDB How to create a User with ReadWriteAnyDatabase role but exclude the admin database
body: <p>I'm trying to create an extended role that allows
  - read/write on any database
  - allow collMod on any database
  - allow createCollection on any database
  - readonly on admin database</p>
  
  <p>I tried the following</p>
  
  <pre><code>use admin
  db.runCommand({ createRole: "_ReadWriteAnyDatabase",
    privileges: [
      { resource: { db: "", collection: "" }, actions: [ "collMod", "createCollection" ] }
    ],
    roles: [
      "readWriteAnyDatabase",
      { role: "read", db : "admin" }
    ]
  })
  </code></pre>
  
  <p>then I created the user on the admin database, because I wasn't able to create the user on an alternative database</p>
  
  <p>but i found out that I can create and delete collections on the admin database</p>
  
  <pre><code>mongo admin -u user1 -p user1
  db.createCollection('mycollection')
  { ok : 1 }
  db.mycollection.drop()
  { ok : 1 }
  </code></pre>