auth.py

#!/usr/bin/env python

# -----------------------------------------------------------------------
# auth.py
# Author: Bob Dondero
# -----------------------------------------------------------------------

from urllib.request import urlopen
from urllib.parse import quote
from re import sub

from flask import request, redirect
from flask import session, abort

# -----------------------------------------------------------------------

# Authors: Modified by Jeremy Dapaah

# -----------------------------------------------------------------------

_CAS_URL = 'https://cast.cs.princeton.edu/cas/'


# -----------------------------------------------------------------------

# Return url after stripping out the "ticket" parameter that was
# added by the CAS server.

def strip_ticket(url):
    if url is None:
        return "something is badly wrong"
    url = sub(r'ticket=[^&]*&?', '', url)
    url = sub(r'\?&?$|&$', '', url)
    return url


# -----------------------------------------------------------------------

# Validate a login ticket by contacting the CAS server. If
# valid, return the user's username; otherwise, return None.

def validate(ticket):
    val_url = (_CAS_URL + "validate"
               + '?service=' + quote(strip_ticket(request.url))
               + '&ticket=' + quote(ticket))
    with urlopen(val_url) as flo:
        lines = flo.readlines()  # Should return 2 lines.
    if len(lines) != 2:
        return None
    first_line = lines[0].decode('utf-8')
    second_line = lines[1].decode('utf-8').strip()
    if not first_line.startswith('yes'):
        return None
    return second_line


# -----------------------------------------------------------------------

# Authenticate the remote user, and return the user's username.
# Do not return unless the user is successfully authenticated.

def authenticate():
    # If the username is in the session, then the user was
    # authenticated previously.  So return the username.
    if 'username' in session:
        return session.get('username')

    # If the request does not contain a login ticket, then redirect
    # the browser to the login page to get one.
    ticket = request.args.get('ticket')
    if ticket is None:
        login_url = (_CAS_URL + 'login?service=' + quote(request.url))
        abort(redirect(login_url))

    # If the login ticket is invalid, then redirect the browser
    # to the login page to get a new one.
    username = validate(ticket)
    if username is None:
        login_url = (_CAS_URL + 'login?service='
                     + quote(strip_ticket(request.url)))
        abort(redirect(login_url))

    # The user is authenticated, so store the username in
    # the session.
    session['username'] = username
    return username


# -----------------------------------------------------------------------

def logout():
    authenticate()

    # Delete the user's username from the session.
    session.pop('username')

    # Logout, and redirect the browser to the index page.
    logout_url = (_CAS_URL + 'logout?service='
                  + quote(sub('logout', 'index', request.url)))
    abort(redirect(logout_url))