Fix Auth0 500 error when not configured (Issue #5)

- Add check for AUTH0 credentials before attempting login
- Show friendly error message if Auth0 not configured
- Hide Auth0 button on login page when not configured
- Add try/catch for auth0.authorize_redirect() failures

Fixes #5

app.py

@@ -704,6 +704,9 @@ def login():
     if current_user.is_authenticated:
         return redirect(url_for('index'))
 
+    # Check if Auth0 is configured
+    auth0_configured = bool(app.config.get('AUTH0_DOMAIN') and app.config.get('AUTH0_CLIENT_ID'))
+
     if request.method == 'POST':
         username = request.form.get('username')
         password = request.form.get('password')
@@ -711,7 +714,7 @@ def login():
 
         if not user_service:
             flash('User service not available', 'error')
-            return render_template('login.html')
+            return render_template('login.html', auth0_configured=auth0_configured)
 
         user = user_service.authenticate(username, password)
 
@@ -725,7 +728,7 @@ def login():
         else:
             flash('Invalid username or password', 'error')
 
-    return render_template('login.html')
+    return render_template('login.html', auth0_configured=auth0_configured)
 
 
 @app.route('/password-reset-request', methods=['GET', 'POST'])
@@ -804,8 +807,18 @@ def password_reset(token):
 @app.route('/auth0/login')
 def auth0_login():
     """Redirect to Auth0 for authentication"""
-    redirect_uri = url_for('auth0_callback', _external=True)
-    return auth0.authorize_redirect(redirect_uri)
+    # Check if Auth0 is configured
+    if not app.config.get('AUTH0_DOMAIN') or not app.config.get('AUTH0_CLIENT_ID'):
+        flash('Auth0 authentication is not configured. Please use email/password login or contact the administrator.', 'error')
+        return redirect(url_for('login'))
+
+    try:
+        redirect_uri = url_for('auth0_callback', _external=True)
+        return auth0.authorize_redirect(redirect_uri)
+    except Exception as e:
+        logger.error(f"Auth0 login error: {e}")
+        flash('Auth0 authentication failed. Please use email/password login.', 'error')
+        return redirect(url_for('login'))
 
 
 @app.route('/auth0/callback')