Add support for 'next' URL parameter for redirect after auth

main.py

@@ -84,10 +84,16 @@ def login_page() -> str | werkzeug.Response:
         # Login failed: Show an error message on the login page
         return flask.render_template("login.html", error="Invalid credentials")
 
+    redirect_to = (
+        flask.request.args.get("next")
+        or flask.session.get("next")
+        or flask.url_for("dashboard")
+    )
+
     expire_date = datetime.now() + timedelta(days=180)
     flask.flash("Welcome back! You have successfully logged in.")
 
-    response = flask.redirect(flask.session.get("next") or flask.url_for("dashboard"))
+    response = flask.redirect(redirect_to)
     response.set_cookie(
         "auth_token",
         generate_auth_token(user["username"]),