Default-deny access control with group flags and access enumeration

Replaces the implicit "empty allowed_groups means public" rule with
explicit default-deny across both OIDC and ForwardAuth. Adds two boolean
flags on Group — auto_assign (Keycloak-style auto-join on user create)
and admin (members can reach the admin panel) — and drops the
users.admin column entirely. Adds "Users with access" and "Accessible
applications" panels with via-group badges on the application/user show
pages.

BEHAVIOR CHANGE: a ForwardAuth app with no allowed_groups previously
bypassed authentication entirely; it now returns 403 like any other
unauthorized request. The data migration seeds an "everyone" group and
attaches it to all previously group-less apps to preserve behavior on
existing installs. An "admins" group is seeded and backfilled from any
user with the old admin column.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/controllers/admin/applications_controller.rb

@@ -8,6 +8,12 @@ module Admin
 
     def show
       @allowed_groups = @application.allowed_groups
+      @users_with_access = User.where(status: User.statuses[:active])
+        .joins(groups: :applications)
+        .where(applications: {id: @application.id})
+        .distinct
+        .includes(:groups)
+        .order(:email_address)
     end
 
     def new

app/controllers/admin/groups_controller.rb

@@ -122,7 +122,7 @@ module Admin
     end
 
     def group_params
-      params.require(:group).permit(:name, :description, :custom_claims)
+      params.require(:group).permit(:name, :description, :custom_claims, :auto_assign, :admin)
     end
   end
 end

app/controllers/admin/users_controller.rb

@@ -7,27 +7,38 @@ module Admin
     end
 
     def show
+      @accessible_applications = Application.where(active: true)
+        .joins(:allowed_groups)
+        .where(groups: {id: @user.groups})
+        .distinct
+        .includes(:allowed_groups)
+        .order(:name)
     end
 
     def new
       @user = User.new
+      @available_groups = Group.order(:name)
     end
 
     def create
       @user = User.new(user_params)
       @user.password = SecureRandom.alphanumeric(16) if user_params[:password].blank?
       @user.status = :pending_invitation
+      @user.skip_auto_assign = true if params[:auto_assign] == "0"
 
       if @user.save
+        assign_groups_from_params(@user)
         InvitationsMailer.invite_user(@user).deliver_later
         redirect_to admin_users_path, notice: "User created successfully. Invitation email sent to #{@user.email_address}."
       else
+        @available_groups = Group.order(:name)
         render :new, status: :unprocessable_entity
       end
     end
 
     def edit
       @applications = Application.active.order(:name)
+      @available_groups = Group.order(:name)
     end
 
     def update
@@ -43,6 +54,7 @@ module Admin
         rescue JSON::ParserError
           @user.errors.add(:custom_claims, "must be valid JSON")
           @applications = Application.active.order(:name)
+          @available_groups = Group.order(:name)
           render :edit, status: :unprocessable_entity
           return
         end
@@ -52,9 +64,16 @@ module Admin
       end
 
       if @user.update(update_params)
+        unless assign_groups_from_params(@user)
+          @applications = Application.active.order(:name)
+          @available_groups = Group.order(:name)
+          render :edit, status: :unprocessable_entity
+          return
+        end
         redirect_to admin_users_path, notice: "User updated successfully."
       else
         @applications = Application.active.order(:name)
+        @available_groups = Group.order(:name)
         render :edit, status: :unprocessable_entity
       end
     end
@@ -122,14 +141,28 @@ module Admin
     end
 
     def user_params
-      permitted = [:email_address, :username, :name, :password, :status, :totp_required, :custom_claims]
+      params.require(:user).permit(:email_address, :username, :name, :password, :status, :totp_required, :custom_claims)
+    end
 
-      # Only allow modifying admin status when editing other users (prevent self-demotion)
-      if params[:id] != Current.session.user.id.to_s
-        permitted << :admin
+    # Apply group_ids from the form, with a guard preventing self-demotion when
+    # the user is the last member of the last admin group. Returns true on
+    # success, false if a guard fired (caller should re-render).
+    def assign_groups_from_params(user)
+      return true unless params[:user].key?(:group_ids)
+
+      raw_ids = Array(params[:user][:group_ids]).reject(&:blank?).map(&:to_i)
+      new_groups = Group.where(id: raw_ids)
+
+      if user == Current.session.user
+        losing_admin = user.groups.where(admin: true).any? && new_groups.none?(&:admin?)
+        if losing_admin
+          user.errors.add(:base, "you cannot remove yourself from all administrator groups")
+          return false
+        end
       end
 
-      params.require(:user).permit(*permitted)
+      user.groups = new_groups
+      true
     end
   end
 end

app/controllers/users_controller.rb

@@ -8,12 +8,16 @@ class UsersController < ApplicationController
 
   def create
     @user = User.new(user_params)
-
-    # First user becomes admin automatically
-    @user.admin = true if User.count.zero?
     @user.status = "active"
+    first_user = User.count.zero?
 
     if @user.save
+      # First user automatically becomes a member of every admin group, so they
+      # can reach the admin panel without an existing admin to grant access.
+      if first_user
+        Group.where(admin: true).each { |g| @user.groups << g }
+      end
+
       start_new_session_for @user
       redirect_to root_path, notice: "Welcome to Clinch! Your account has been created."
     else

app/models/application.rb

@@ -118,14 +118,12 @@ class Application < ApplicationRecord
   end
 
   # Access control
+  # Default-deny: an empty allowed_groups list means no one gets in.
+  # To make an app accessible to "everyone", attach the seeded auto-assign
+  # group (or any group every user is in).
   def user_allowed?(user)
     return false unless active?
     return false unless user.active?
-
-    # If no groups are specified, allow all active users
-    return true if allowed_groups.empty?
-
-    # Otherwise, user must be in at least one of the allowed groups
     (user.groups & allowed_groups).any?
   end
 
@@ -168,10 +166,6 @@ class Application < ApplicationRecord
     return "deny" unless active?
     return "deny" unless user.active?
 
-    # If no groups specified, bypass authentication
-    return "bypass" if allowed_groups.empty?
-
-    # If user is in allowed groups, determine auth level
     if user_allowed?(user)
       # Require 2FA if user has TOTP configured, otherwise one factor
       user.totp_enabled? ? "two_factor" : "one_factor"

app/models/group.rb

@@ -15,6 +15,11 @@ class Group < ApplicationRecord
   normalizes :name, with: ->(name) { name.strip.downcase }
   validate :no_reserved_claim_names
 
+  scope :auto_assign, -> { where(auto_assign: true) }
+  scope :admin, -> { where(admin: true) }
+
+  before_destroy :ensure_other_admin_group_exists
+
   # Parse custom_claims JSON field
   def parsed_custom_claims
     return {} if custom_claims.blank?
@@ -23,6 +28,13 @@ class Group < ApplicationRecord
 
   private
 
+  def ensure_other_admin_group_exists
+    return unless admin?
+    return if Group.where(admin: true).where.not(id: id).exists?
+    errors.add(:base, "cannot delete the last administrators group")
+    throw :abort
+  end
+
   def no_reserved_claim_names
     return if custom_claims.blank?
 

app/models/user.rb

@@ -42,7 +42,18 @@ class User < ApplicationRecord
   enum :status, {active: 0, disabled: 1, pending_invitation: 2}
 
   # Scopes
-  scope :admins, -> { where(admin: true) }
+  scope :admins, -> { joins(:groups).where(groups: {admin: true}).distinct }
+
+  # Set true on a user (or on the user_params) to skip the auto-assign callback
+  # for that record. Used by the admin invite form (opt-out checkbox) and by
+  # tests that want a clean slate.
+  attr_accessor :skip_auto_assign
+
+  after_create :add_to_auto_assign_groups, unless: :skip_auto_assign
+
+  def admin?
+    groups.any?(&:admin?)
+  end
 
   # TOTP methods
   def totp_enabled?
@@ -222,6 +233,10 @@ class User < ApplicationRecord
 
   private
 
+  def add_to_auto_assign_groups
+    Group.auto_assign.each { |g| groups << g }
+  end
+
   def no_reserved_claim_names
     return if custom_claims.blank?
 

app/views/admin/applications/show.html.erb

@@ -274,11 +274,11 @@
         <dt class="text-sm font-medium text-gray-500 dark:text-gray-400 mb-2">Allowed Groups</dt>
         <dd class="mt-1 text-sm text-gray-900 dark:text-gray-100">
           <% if @allowed_groups.empty? %>
-            <div class="rounded-md bg-blue-50 dark:bg-blue-900/30 p-4">
+            <div class="rounded-md bg-amber-50 dark:bg-amber-900/30 p-4">
               <div class="flex">
                 <div class="ml-3">
-                  <p class="text-sm text-blue-700 dark:text-blue-300">
-                    No groups assigned - all active users can access this application.
+                  <p class="text-sm text-amber-700 dark:text-amber-300">
+                    No groups assigned — no one can access this application. Attach a group to grant access.
                   </p>
                 </div>
               </div>
@@ -299,4 +299,35 @@
       </div>
     </div>
   </div>
+
+  <!-- Users with access -->
+  <div class="bg-white dark:bg-gray-800 shadow sm:rounded-lg">
+    <div class="px-4 py-5 sm:p-6">
+      <h3 class="text-base font-semibold leading-6 text-gray-900 dark:text-gray-100 mb-4">
+        Users with access (<%= @users_with_access.count %>)
+      </h3>
+      <% if @users_with_access.any? %>
+        <ul class="divide-y divide-gray-200 dark:divide-gray-700 border border-gray-200 dark:border-gray-700 rounded-md">
+          <% @users_with_access.each do |user| %>
+            <% via = user.groups & @application.allowed_groups %>
+            <li class="px-4 py-3 flex items-center justify-between">
+              <div>
+                <p class="text-sm font-medium text-gray-900 dark:text-gray-100"><%= user.email_address %></p>
+                <div class="flex flex-wrap gap-1 mt-1">
+                  <% via.each do |g| %>
+                    <span class="inline-flex items-center rounded-full bg-gray-100 dark:bg-gray-700 px-2 py-0.5 text-xs font-medium text-gray-700 dark:text-gray-300">via <%= g.name %></span>
+                  <% end %>
+                </div>
+              </div>
+              <%= link_to "View", admin_user_path(user), class: "text-blue-600 hover:text-blue-900 text-sm" %>
+            </li>
+          <% end %>
+        </ul>
+      <% else %>
+        <div class="rounded-md bg-gray-50 dark:bg-gray-700 p-4">
+          <p class="text-sm text-gray-500 dark:text-gray-400">No users currently have access. Attach a group to grant access.</p>
+        </div>
+      <% end %>
+    </div>
+  </div>
 </div>

app/views/admin/groups/_form.html.erb

@@ -12,6 +12,22 @@
     <%= form.text_area :description, rows: 3, class: "mt-1 block w-full rounded-md border-gray-300 dark:border-gray-600 dark:bg-gray-800 dark:text-gray-100 shadow-sm focus:border-blue-500 focus:ring-blue-500 sm:text-sm", placeholder: "Optional description of this group" %>
   </div>
 
+  <div>
+    <div class="flex items-center">
+      <%= form.check_box :auto_assign, class: "h-4 w-4 rounded border-gray-300 dark:border-gray-600 text-blue-600 focus:ring-blue-500" %>
+      <%= form.label :auto_assign, "Auto Assign", class: "ml-2 text-sm text-gray-900 dark:text-gray-100" %>
+    </div>
+    <p class="mt-1 text-sm text-gray-500 dark:text-gray-400">New users will be automatically added to this group when invited. You can mark multiple groups as auto-assigned.</p>
+  </div>
+
+  <div>
+    <div class="flex items-center">
+      <%= form.check_box :admin, class: "h-4 w-4 rounded border-gray-300 dark:border-gray-600 text-blue-600 focus:ring-blue-500" %>
+      <%= form.label :admin, "Administrators", class: "ml-2 text-sm text-gray-900 dark:text-gray-100" %>
+    </div>
+    <p class="mt-1 text-sm text-gray-500 dark:text-gray-400">Members of this group can access the admin panel. Does not grant automatic access to applications.</p>
+  </div>
+
   <div>
     <%= form.label :user_ids, "Group Members", class: "block text-sm font-medium text-gray-700 dark:text-gray-300" %>
     <div class="mt-2 space-y-2 max-h-64 overflow-y-auto border border-gray-200 dark:border-gray-700 rounded-md p-3">

app/views/admin/groups/show.html.erb

@@ -1,7 +1,15 @@
 <div class="mb-6">
   <div class="sm:flex sm:items-center sm:justify-between">
     <div>
-      <h1 class="text-2xl font-semibold text-gray-900 dark:text-gray-100"><%= @group.name %></h1>
+      <div class="flex items-center gap-2">
+        <h1 class="text-2xl font-semibold text-gray-900 dark:text-gray-100"><%= @group.name %></h1>
+        <% if @group.auto_assign? %>
+          <span class="inline-flex items-center rounded-full bg-green-100 dark:bg-green-900/50 px-2 py-0.5 text-xs font-medium text-green-700 dark:text-green-300">Auto Assign</span>
+        <% end %>
+        <% if @group.admin? %>
+          <span class="inline-flex items-center rounded-full bg-blue-100 dark:bg-blue-900/50 px-2 py-0.5 text-xs font-medium text-blue-700 dark:text-blue-300">Administrators</span>
+        <% end %>
+      </div>
       <% if @group.description.present? %>
         <p class="mt-1 text-sm text-gray-500 dark:text-gray-400"><%= @group.description %></p>
       <% end %>

app/views/admin/users/_form.html.erb

@@ -33,11 +33,36 @@
     <%= form.select :status, User.statuses.keys.map { |s| [s.titleize, s] }, {}, class: "mt-1 block w-full rounded-md border-gray-300 dark:border-gray-600 dark:bg-gray-800 dark:text-gray-100 shadow-sm focus:border-blue-500 focus:ring-blue-500 sm:text-sm" %>
   </div>
 
-  <div class="flex items-center">
-    <%= form.check_box :admin, class: "h-4 w-4 rounded border-gray-300 dark:border-gray-600 text-blue-600 focus:ring-blue-500", disabled: (user == Current.session.user) %>
-    <%= form.label :admin, "Administrator", class: "ml-2 block text-sm text-gray-900 dark:text-gray-100" %>
-    <% if user == Current.session.user %>
-      <span class="ml-2 text-xs text-gray-500 dark:text-gray-400">(Cannot change your own admin status)</span>
+  <div>
+    <%= form.label :group_ids, "Group Memberships", class: "block text-sm font-medium text-gray-700 dark:text-gray-300" %>
+    <div class="mt-2 space-y-2 max-h-64 overflow-y-auto border border-gray-200 dark:border-gray-700 rounded-md p-3">
+      <% if @available_groups.any? %>
+        <% @available_groups.each do |group| %>
+          <div class="flex items-center">
+            <%= check_box_tag "user[group_ids][]", group.id, user.groups.include?(group), class: "h-4 w-4 rounded border-gray-300 dark:border-gray-600 text-blue-600 focus:ring-blue-500" %>
+            <%= label_tag "user_group_ids_#{group.id}", group.name, class: "ml-2 text-sm text-gray-900 dark:text-gray-100" %>
+            <% if group.admin? %>
+              <span class="ml-2 inline-flex items-center rounded-full bg-blue-100 dark:bg-blue-900/50 px-2 py-0.5 text-xs font-medium text-blue-700 dark:text-blue-300">Admin</span>
+            <% end %>
+            <% if group.auto_assign? %>
+              <span class="ml-2 inline-flex items-center rounded-full bg-green-100 dark:bg-green-900/50 px-2 py-0.5 text-xs font-medium text-green-700 dark:text-green-300">Auto Assign</span>
+            <% end %>
+          </div>
+        <% end %>
+      <% else %>
+        <p class="text-sm text-gray-500 dark:text-gray-400">No groups available. Create a group first.</p>
+      <% end %>
+    </div>
+    <p class="mt-1 text-sm text-gray-500 dark:text-gray-400">Administrators are members of any group with the Admin flag set. You cannot remove yourself from your last administrator group.</p>
+    <% unless user.persisted? %>
+      <% auto_names = Group.where(auto_assign: true).pluck(:name) %>
+      <% if auto_names.any? %>
+        <div class="mt-2 flex items-center">
+          <%= check_box_tag "auto_assign", "1", true, class: "h-4 w-4 rounded border-gray-300 dark:border-gray-600 text-blue-600 focus:ring-blue-500" %>
+          <%= label_tag "auto_assign", "Auto-assign to default groups (#{auto_names.join(", ")})", class: "ml-2 text-sm text-gray-900 dark:text-gray-100" %>
+        </div>
+        <p class="mt-1 text-xs text-gray-500 dark:text-gray-400">Uncheck to invite this user without auto-assigning the default group(s) — useful for restricted accounts.</p>
+      <% end %>
     <% end %>
   </div>
 

app/views/admin/users/show.html.erb

@@ -0,0 +1,95 @@
+<div class="mb-6">
+  <div class="sm:flex sm:items-center sm:justify-between">
+    <div>
+      <div class="flex items-center gap-2">
+        <h1 class="text-2xl font-semibold text-gray-900 dark:text-gray-100"><%= @user.email_address %></h1>
+        <% if @user.admin? %>
+          <span class="inline-flex items-center rounded-full bg-blue-100 dark:bg-blue-900/50 px-2 py-0.5 text-xs font-medium text-blue-700 dark:text-blue-300">Admin</span>
+        <% end %>
+        <% case @user.status %>
+        <% when "active" %>
+          <span class="inline-flex items-center rounded-full bg-green-100 dark:bg-green-900/50 px-2 py-0.5 text-xs font-medium text-green-700 dark:text-green-300">Active</span>
+        <% when "disabled" %>
+          <span class="inline-flex items-center rounded-full bg-gray-100 dark:bg-gray-700 px-2 py-0.5 text-xs font-medium text-gray-700 dark:text-gray-300">Disabled</span>
+        <% when "pending_invitation" %>
+          <span class="inline-flex items-center rounded-full bg-amber-100 dark:bg-amber-900/50 px-2 py-0.5 text-xs font-medium text-amber-700 dark:text-amber-300">Pending Invitation</span>
+        <% end %>
+      </div>
+      <% if @user.name.present? %>
+        <p class="mt-1 text-sm text-gray-500 dark:text-gray-400"><%= @user.name %></p>
+      <% end %>
+    </div>
+    <div class="mt-4 sm:mt-0 flex gap-3">
+      <%= link_to "Edit", edit_admin_user_path(@user), class: "rounded-md bg-white dark:bg-gray-700 px-3 py-2 text-sm font-semibold text-gray-900 dark:text-gray-200 shadow-sm ring-1 ring-inset ring-gray-300 dark:ring-gray-600 hover:bg-gray-50 dark:hover:bg-gray-600" %>
+    </div>
+  </div>
+</div>
+
+<div class="space-y-6">
+  <!-- Group memberships -->
+  <div class="bg-white dark:bg-gray-800 shadow sm:rounded-lg">
+    <div class="px-4 py-5 sm:p-6">
+      <h3 class="text-base font-semibold leading-6 text-gray-900 dark:text-gray-100 mb-4">
+        Group memberships (<%= @user.groups.count %>)
+      </h3>
+      <% if @user.groups.any? %>
+        <ul class="divide-y divide-gray-200 dark:divide-gray-700 border border-gray-200 dark:border-gray-700 rounded-md">
+          <% @user.groups.order(:name).each do |group| %>
+            <li class="px-4 py-3 flex items-center justify-between">
+              <div class="flex items-center gap-2">
+                <p class="text-sm font-medium text-gray-900 dark:text-gray-100"><%= group.name %></p>
+                <% if group.admin? %>
+                  <span class="inline-flex items-center rounded-full bg-blue-100 dark:bg-blue-900/50 px-2 py-0.5 text-xs font-medium text-blue-700 dark:text-blue-300">Admin</span>
+                <% end %>
+                <% if group.auto_assign? %>
+                  <span class="inline-flex items-center rounded-full bg-green-100 dark:bg-green-900/50 px-2 py-0.5 text-xs font-medium text-green-700 dark:text-green-300">Auto Assign</span>
+                <% end %>
+              </div>
+              <%= link_to "View", admin_group_path(group), class: "text-blue-600 hover:text-blue-900 text-sm" %>
+            </li>
+          <% end %>
+        </ul>
+      <% else %>
+        <p class="text-sm text-gray-500 dark:text-gray-400">This user is in no groups.</p>
+      <% end %>
+    </div>
+  </div>
+
+  <!-- Accessible applications -->
+  <div class="bg-white dark:bg-gray-800 shadow sm:rounded-lg">
+    <div class="px-4 py-5 sm:p-6">
+      <h3 class="text-base font-semibold leading-6 text-gray-900 dark:text-gray-100 mb-4">
+        Accessible applications (<%= @accessible_applications.count %>)
+      </h3>
+      <% unless @user.active? %>
+        <div class="rounded-md bg-amber-50 dark:bg-amber-900/30 p-4">
+          <p class="text-sm text-amber-700 dark:text-amber-300">
+            User is <%= @user.status.humanize.downcase %> — access is denied regardless of group memberships.
+          </p>
+        </div>
+      <% end %>
+      <% if @accessible_applications.any? %>
+        <ul class="divide-y divide-gray-200 dark:divide-gray-700 border border-gray-200 dark:border-gray-700 rounded-md">
+          <% @accessible_applications.each do |app| %>
+            <% via = app.allowed_groups & @user.groups %>
+            <li class="px-4 py-3 flex items-center justify-between">
+              <div>
+                <p class="text-sm font-medium text-gray-900 dark:text-gray-100"><%= app.name %></p>
+                <div class="flex flex-wrap gap-1 mt-1">
+                  <% via.each do |g| %>
+                    <span class="inline-flex items-center rounded-full bg-gray-100 dark:bg-gray-700 px-2 py-0.5 text-xs font-medium text-gray-700 dark:text-gray-300">via <%= g.name %></span>
+                  <% end %>
+                </div>
+              </div>
+              <%= link_to "View", admin_application_path(app), class: "text-blue-600 hover:text-blue-900 text-sm" %>
+            </li>
+          <% end %>
+        </ul>
+      <% else %>
+        <div class="rounded-md bg-gray-50 dark:bg-gray-700 p-4">
+          <p class="text-sm text-gray-500 dark:text-gray-400">No accessible applications. Add the user to a group that's attached to one or more applications.</p>
+        </div>
+      <% end %>
+    </div>
+  </div>
+</div>