diff --git a/lib/models/acl.js b/lib/models/acl.js
index 07a941c0..6b3f6d46 100644
--- a/lib/models/acl.js
+++ b/lib/models/acl.js
@@ -29,4 +29,15 @@ URL/Route level permissions
 
 Map to oAuth 2.0 scopes
 
-*/
\ No newline at end of file
+*/
+
+var ACLSchema = {
+    model: String, // The model name
+    properties: [String], // A list of property names
+    methods: [String], // A list of methods
+    roles: [String], // A list of roles
+    permission: {type: String, enum: ['Allow', 'Deny']}, // Allow/Deny
+    status: String, // Enabled/disabled
+    created: Date,
+    lastUpdated: Date
+}
\ No newline at end of file
diff --git a/lib/models/installation.js b/lib/models/installation.js
index 37e8bd0d..03d1b0ed 100644
--- a/lib/models/installation.js
+++ b/lib/models/installation.js
@@ -1,4 +1,4 @@
-// Device registration
+// See Device registration
 var InstallationSchema = {
 
 };
diff --git a/lib/models/role.js b/lib/models/role.js
index a04ad962..0bd17dae 100644
--- a/lib/models/role.js
+++ b/lib/models/role.js
@@ -4,7 +4,6 @@ var RoleSchema = {
     name: {type: String, required: true},
     roles: [String], // A role can be an aggregate of other roles
     users: [String], // A role contains a list of users
-    acls: [],
 
     created: Date,
     lastUpdated: Date
diff --git a/lib/models/user.js b/lib/models/user.js
index ec63821a..545e772c 100644
--- a/lib/models/user.js
+++ b/lib/models/user.js
@@ -1,9 +1,22 @@
+var ChallengeSchema = {
+    // id: String,
+    question: String,
+    answer: String
+};
+
+var Credential = {
+    // id: String,
+    provider: String,
+    protocol: String,
+    attributes: Object
+}
+
 // User model
 var UserSchema = {
     id: {type: String, required: true},
     realm: {type: String},
     username: {type: String, required: true},
-    password: {type: String, transient: true}, // Transient property
+    // password: {type: String, transient: true}, // Transient property
     hash: {type: String}, // Hash code calculated from sha256(realm, username, password, salt, macKey)
     salt: {type: String},
     macKey: {type: String}, // HMAC to calculate the hash code
@@ -15,6 +28,12 @@ var UserSchema = {
     challenges: [
         'Challenge' // Security questions/answers
     ],
+    // https://en.wikipedia.org/wiki/Multi-factor_authentication
+    /*
+    factors: [
+        'AuthenticationFactor'
+    ],
+    */
     status: String,
     created: Date,
     lastUpdated: Date