Gate registration behind the site setting; land on dashboard after login

app/routes/auth.py

@@ -2,6 +2,7 @@ from flask import Blueprint, render_template, redirect, url_for, flash, request
 from flask_login import login_user, logout_user, login_required, current_user
 from app import db
 from app.models.user import User
+from app.models.site_setting import SiteSetting
 
 auth_bp = Blueprint('auth', __name__, url_prefix='/auth')
 
@@ -12,6 +13,14 @@ def register():
     if current_user.is_authenticated:
         return redirect(url_for('main.index'))
 
+    # Admins can close signups from Site Settings. The very first account is
+    # always allowed through, otherwise a fresh install locks itself out.
+    if not SiteSetting.get_bool('allow_registration', True) and \
+            User.query.first() is not None:
+        flash('Registration is currently closed. Ask an administrator for an account.',
+              'warning')
+        return redirect(url_for('auth.login'))
+    
     if request.method == 'POST':
         username = request.form.get('username')
         email = request.form.get('email')
@@ -74,7 +83,7 @@ def login():
             login_user(user, remember=bool(remember))
             next_page = request.args.get('next')
             flash(f'Welcome back, {user.username}!', 'success')
-            return redirect(next_page) if next_page else redirect(url_for('main.index'))
+            return redirect(next_page) if next_page else redirect(url_for('main.dashboard'))
         else:
             flash('Invalid username or password.', 'danger')