ScoDoc/flask_cas/routing.py

import ssl

import flask
from xmltodict import parse
from flask import current_app
from .cas_urls import create_cas_login_url
from .cas_urls import create_cas_logout_url
from .cas_urls import create_cas_validate_url


try:
    from urllib import urlopen  # python 2
except ImportError:
    from urllib.request import urlopen  # python 3
from urllib.error import URLError

blueprint = flask.Blueprint("cas", __name__)


@blueprint.route("/login/")
def login():
    """
    This route has two purposes. First, it is used by the user
    to login. Second, it is used by the CAS to respond with the
    `ticket` after the user logs in successfully.

    When the user accesses this url, they are redirected to the CAS
    to login. If the login was successful, the CAS will respond to this
    route with the ticket in the url. The ticket is then validated.
    If validation was successful the logged in username is saved in
    the user's session under the key `CAS_USERNAME_SESSION_KEY` and
    the user's attributes are saved under the key
    'CAS_USERNAME_ATTRIBUTE_KEY'
    """

    cas_token_session_key = current_app.config["CAS_TOKEN_SESSION_KEY"]

    redirect_url = create_cas_login_url(
        current_app.config["CAS_SERVER"],
        current_app.config["CAS_LOGIN_ROUTE"],
        flask.url_for(
            ".login",
            origin=flask.session.get("CAS_AFTER_LOGIN_SESSION_URL"),
            _external=True,
        ),
    )

    if "ticket" in flask.request.args:
        flask.session[cas_token_session_key] = flask.request.args["ticket"]

    if cas_token_session_key in flask.session:

        if validate(flask.session[cas_token_session_key]):
            if "CAS_AFTER_LOGIN_SESSION_URL" in flask.session:
                redirect_url = flask.session.pop("CAS_AFTER_LOGIN_SESSION_URL")
            elif flask.request.args.get("origin"):
                redirect_url = flask.request.args["origin"]
            else:
                redirect_url = flask.url_for(current_app.config["CAS_AFTER_LOGIN"])
        else:
            flask.session.pop(cas_token_session_key, None)

    current_app.logger.debug("Redirecting to: {0}".format(redirect_url))

    return flask.redirect(redirect_url)


@blueprint.route("/logout/")
def logout():
    """
    When the user accesses this route they are logged out.
    """

    cas_username_session_key = current_app.config["CAS_USERNAME_SESSION_KEY"]
    cas_attributes_session_key = current_app.config["CAS_ATTRIBUTES_SESSION_KEY"]
    cas_token_session_key = current_app.config["CAS_TOKEN_SESSION_KEY"]

    flask.session.pop(cas_username_session_key, None)
    flask.session.pop(cas_attributes_session_key, None)
    flask.session.pop(cas_token_session_key, None)  # added by EV

    cas_after_logout = current_app.config["CAS_AFTER_LOGOUT"]
    if cas_after_logout is not None:
        # If config starts with http, use it as dest URL.
        # Else, build Flask URL
        dest_url = (
            cas_after_logout
            if cas_after_logout.startswith("http")
            else flask.url_for(cas_after_logout, _external=True)
        )
        redirect_url = create_cas_logout_url(
            current_app.config["CAS_SERVER"],
            current_app.config["CAS_LOGOUT_ROUTE"],
            dest_url,
        )
    else:
        redirect_url = create_cas_logout_url(
            current_app.config["CAS_SERVER"], current_app.config["CAS_LOGOUT_ROUTE"]
        )

    current_app.logger.debug("Redirecting to: {0}".format(redirect_url))
    return flask.redirect(redirect_url)


def validate(ticket):
    """
    Will attempt to validate the ticket. If validation fails, then False
    is returned. If validation is successful, then True is returned
    and the validated username is saved in the session under the
    key `CAS_USERNAME_SESSION_KEY` while tha validated attributes dictionary
    is saved under the key 'CAS_ATTRIBUTES_SESSION_KEY'.
    """

    cas_username_session_key = current_app.config["CAS_USERNAME_SESSION_KEY"]
    cas_attributes_session_key = current_app.config["CAS_ATTRIBUTES_SESSION_KEY"]

    current_app.logger.debug("validating token {0}".format(ticket))

    cas_validate_url = create_cas_validate_url(
        current_app.config["CAS_SERVER"],
        current_app.config["CAS_VALIDATE_ROUTE"],
        flask.url_for(
            ".login",
            origin=flask.session.get("CAS_AFTER_LOGIN_SESSION_URL"),
            _external=True,
        ),
        ticket,
    )

    current_app.logger.debug("Making GET request to {0}".format(cas_validate_url))

    xml_from_dict = {}
    isValid = False

    if current_app.config.get("CAS_SSL_VERIFY"):
        ssl_context = ssl.SSLContext()
        ssl_context.verify_mode = ssl.CERT_REQUIRED
        ca_data = current_app.config.get("CAS_SSL_CERTIFICATE", "")
        try:
            ssl_context.load_verify_locations(cadata=ca_data)
        except (ssl.SSLError, ValueError):
            current_app.logger.error("CAS : error loading SSL cert.")
            return False
    else:
        ssl_context = None

    try:
        xmldump = (
            urlopen(cas_validate_url, context=ssl_context)
            .read()
            .strip()
            .decode("utf8", "ignore")
        )
        xml_from_dict = parse(xmldump)
        isValid = (
            True
            if "cas:authenticationSuccess" in xml_from_dict["cas:serviceResponse"]
            else False
        )
    except ValueError:
        current_app.logger.error("CAS returned unexpected result")
    except URLError:
        current_app.logger.error("CAS : error validating token: check SSL certificate")

    if isValid:
        current_app.logger.debug("valid")
        xml_from_dict = xml_from_dict["cas:serviceResponse"][
            "cas:authenticationSuccess"
        ]
        username = xml_from_dict["cas:user"]
        attributes = xml_from_dict.get("cas:attributes", {})

        if attributes and "cas:memberOf" in attributes:
            if isinstance(attributes["cas:memberOf"], basestring):
                attributes["cas:memberOf"] = (
                    attributes["cas:memberOf"].lstrip("[").rstrip("]").split(",")
                )
                for group_number in range(0, len(attributes["cas:memberOf"])):
                    attributes["cas:memberOf"][group_number] = (
                        attributes["cas:memberOf"][group_number].lstrip(" ").rstrip(" ")
                    )
        flask.session[cas_username_session_key] = username
        flask.session[cas_attributes_session_key] = attributes
    else:
        current_app.logger.debug("invalid")

    return isValid