rcs-flask-aad-login

Python package to allow Flask web applications to single sign-on through IC's Azure Active Directory

Provides a package that wraps the necessary extensions and attribute labels to add single sign on through the Imperial College Microsoft Azure Active Directory to a Flask application.

Example

A simple example Flask app (which of course won't work until you've set up your AAD app):

from flask import Flask
from flask_login import login_required
import rcs_flask_aad_login

app = Flask(__name__)
app.config.update({
    # Standard Flask SECRET_KEY.  Must be set or example will fail.
    # python -c 'import os; print(os.urandom(24).encode("hex"))'
    'SECRET_KEY': 'notsecret',
    # Insert your own app's metadata url here.
    'SAML_METADATA_URL': 'https://login.microsoftonline.com/2b897507-ee8c-4575-830b-4f8267c3d307/federationmetadata/2007-06/federationmetadata.xml?appid=a301bd20-6119-40ea-a6e1-4d82f14b5d0e',
})

rcs_flask_aad_login.init_app(app)

@app.route('/')
def index():
    return 'Public info'
    
@app.route('/priv')
@login_required
def priv():
    return """\
secrets<br>
username: %s<br>
username w domain: %s<br>
givenname: %s<br>
surname: %s<br>
displayname: %s<br>
emailaddress: %s""" % (current_user.username, current_user.username_domain,
    current_user.givenname, current_user.surname, current_user.displayname,
    current_user.emailaddress)

if __name__ == '__main__':
    app.run(ssl_context='adhoc', port=5000, debug=True)

To run this in the flask development server you would need to run it as python app.py, rather than using the FLASK_APP flask run method, otherwise the SSL context doesn't load. AAD requires https for the Reply-URL.

With this app the / route is unprotected but the /priv route is only available to logged in users. If someone tries to access /priv who is not signed on, the app will redirect them to the login URL, which redirects them to the AAD single sign on. After authentication they are redirected back to the page they were trying to access. If they have a valid SSO session with AAD this process is seamless.

Installation

pip install git+git://github.com/ImperialCollegeLondon/rcs_flask_aad_login

Setup

from flask import Flask
from flask_login import login_required
import rcs_flask_aad_login

app = Flask(__name__)
app.config.update({
  'SAML_METADATA_URL': 'https://login.microsoftonline.com/2b897507-ee8c-4575-830b-4f8267c3d307/federationmetadata/2007-06/federationmetadata.xml?appid=a301bd20-6119-40ea-a6e1-4d82f14b5d0e',
  'SECRET_KEY': '',
  
rcs_flask_aad_login.init_app(app)

The SAML_METADATA_URL parameter is what MS Azure calls the App Federation Metadata URL. For our app it's found in the MS Azure setup pages at: Home->imperial college london->Enterprise applications->All applications->RCS Self-Service Portal DEV->Single sign-on under '4. SAML Signing Certificate'. On the same page you must fill in 'Indentifier (Entity ID)' to https://<yourappsbaseurl>/saml/metadata/, and 'Reply URL (Assertion Consumer Service URL)' to https://<yourappsbaseurl>/saml/acs/. The latter in particular must be a https URL. Save the page and run Test SAML Settings if desired.

Annoyingly there's another page which must be updated. It is at Home->Imperial College London - App registrations->RCS Self-Service Portal DEV->Settings->Properties. Set the Home Page URL to the base URL of your app. This is checked when your app initiates the sign-on. If it's wrong you'll get errors like Application with identifier 'http://localhost:8080/saml/metadata/' was not found in the directory..., where localhost:8080 is the page of your app you're initiating the SSO from.

Now decorate routes with @login_required. When a user accesses the route they will be redirected through to the AAD single sign on and then redirected back to the page they were requesting. You can provide a login link by using the URL url_for('login') provides, and a logout link from url_for('logout'). The logout link will log the user out of the Flask-login session, but not out of the AAD SSO session, which will expire according to whatever settings it and the user have set. If the user attempts to log in while their SSO session is valid, they will be signed in and returned to the desired page fairly seamlessly.

Accessing user data

When a user authenticates a Flask-login User object is created and populated with data from the IC AAD entry. The current parameters are

username - this is the bare college username.
username_domain - this is the college username with '@ic.ac.uk' appended.
givenname - the forename(s).
surname - the surname.
displayname - the college entry for the full name, usually 'Surname, Forename(s)'.
emailaddress - email address

The current_user variable (from flask_login import current_user) holds the logged in User object or None. Access the parameters as normal: e.g. current_user.username.

Behind the scenes

The package uses the Flask-login and Flask-SAML packages. Flask-login provides a session based login system; decorate private routes in the app with @login_required. When an unauthorised user accesses such a route we send them to the Flask-SAML provided login route (url_for('login'), setting a parameter so that after the SSO sign on they will be redirected back to the page they were trying to access.

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