Cookies, Sessions & Flash Messages

from flask import Flask, session, redirect, url_for, flash

app = Flask(__name__)
# Secret key is required to sign session cookies
app.secret_key = "super-secret-key-change-this-in-prod"

@app.route("/login-session")
def login():
    session["user"] = "Balaji"
    flash("Logged in successfully!", "info")
    return redirect(url_for("profile"))

@app.route("/profile")
def profile():
    user = session.get("user")
    if not user:
        flash("You are not logged in.", "warning")
        return "Please log in first."
    return f"Welcome, {user}!"

{% with messages = get_flashed_messages(with_categories=true) %}
  {% if messages %}
    <div class="flashes">
    {% for category, message in messages %}
      <div class="alert alert-{{ category }}">{{ message }}</div>
    {% endfor %}
    </div>
  {% endif %}
{% endwith %}