An example flask decorator that checks if the current users has 'saml_user' in session and redirects to the login flow if not.

example_saml_auth_decorator.py

from functools import wraps
from flask import request, redirect, url_for

# custom decorator
def check_auth(f):
    @wraps(f)
    def decorated(*args, **kwargs):
        if 'saml_user' not in session:
            return redirect(url_for('login'))
        return func(*args, **kwargs)
    return decorated

# route with decorator
@app.route('/hello/')
@check_auth
def hello():
    return render_template('hello.html')

The check_auth decorator checks if the saml_user is in the session. If it is not present, the user is redirected to the login page. If the saml_user is present, the original function is called.

This code requires python3-saml and have properly added the authenticated user to the session under the key saml_user.