Explicitly treat zero

client/App.vue

@@ -29,11 +29,11 @@
             <h4>Add external users</h4>
             <p>Employees and students are allowed to create external users for collaboration with actors outside of Linköpings University.<br/>
               This application will track and allow creation of such external users, up to a number configurable by the administrators.<br/></p>
-            <button class="btn btn-success" :disabled="user.eum_settings.external_limit > 0 && external.length >= user.eum_settings.external_limit" @click="showCreationForm = !showCreationForm">New External User</button>
+            <button class="btn btn-success" :disabled="user.eum_settings.external_limit >= 0 && external.length >= user.eum_settings.external_limit" @click="showCreationForm = !showCreationForm">New External User</button>
           </div>
         </transition>
 
-        <h2 class="mt-4 mb-3">Existing external users: ({{ external.length }}/<span v-if="user.eum_settings.external_limit > 0">{{ user.eum_settings.external_limit }}</span><span v-else>&infin;</span>)</h2>
+        <h2 class="mt-4 mb-3">Existing external users: ({{ external.length }}/<span v-if="user.eum_settings.external_limit >= 0">{{ user.eum_settings.external_limit }}</span><span v-else>&infin;</span>)</h2>
         <hr/>
         <transition name="fade" mode="out-in">
           <ul class="list-unstyled" is="transition-group" name="flip-list" v-if="external">

server/users.js

@@ -40,6 +40,10 @@ router.post('/', async (req, res) => {
     .reduce( (rs, key) => (rs[key] = req.body[key], rs), {} )
   )
 
+  if (req.user.eum_settings.external_limit == 0) {
+      return res.status(401).send({ 'message': 'No external users allowed' });
+  }
+
   if (req.user.eum_settings.external_limit > 0) {
     try {
       const queryText = 'SELECT * FROM external_users WHERE owner_id = $1';