~azzar1/unity/add-show-desktop-key

# IVLE - Informatics Virtual Learning Environment

# Copyright (C) 2007-2008 The University of Melbourne

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

# Module: authenticate

# Author: Matt Giuca

# Date:   19/2/2008

# Provides a mechanism for authenticating a username and password, and

# returning a yes/no response.

# Has a plugin interface for authentication modules.

# An authentication module is a callable object which accepts 3 positional

# arguments.

# plugin_auth_func(dbconn, login, password, user)

# dbconn is an open connection to the IVLE database.

# login and password are required strings, password is cleartext.

# user is a User object or None.

# If it's a User object, it must return the same object if it returns a user.

# This object should describe the user logging in.

# It may be None if the user is not known to this DB.

# Returns either a User object or None, or raises an AuthError.

# Returning a User object implies success, and also gives details about the

# user if none were known to the DB (such details will be written to the DB).

# Returning None implies a soft failure, and that another auth method should

# be found.

# Raising an AuthError implies a hard failure, with an appropriate error

# message. No more auth will be done.

import conf

import common.db

import common.user

import ldap

class AuthError(Exception):

    def __init__(self, message="Invalid username or password."):

        self.message = message

        self.args = (message,)

def authenticate(login, password):

    """Determines whether a particular login/password combination is

    valid. The password is in cleartext.

    Returns a User object containing the user's details on success.

    Raises an AuthError containing an appropriate error message on failure.

    The User returned is guaranteed to be in the IVLE database.

    This could be from reading or writing to the DB. If authenticate can't

    find the user in the DB, it may get user data from some other source

    (such as LDAP) and actually write it to the DB before returning.

    """

    # WARNING: Both username and password may contain any characters, and must

    # be sanitized within this function.

    # (Not SQL-sanitized, just sanitized to our particular constraints).

    # TODO Sanitize username

    # Spawn a DB object just for making this call.

    # (This should not spawn a DB connection on each page reload, only when

    # there is no session object to begin with).

    dbconn = common.db.DB()

    user = dbconn.get_user(login)

    try:

        for m in auth_modules:

            # May raise an AuthError - allow to propagate

            auth_result = m(dbconn, login, password, user)

            if auth_result is None:

                # Can't auth with this module; try another

                pass

            elif auth_result == False:

                return None

            elif isinstance(auth_result, common.user.User):

                if user is not None and auth_result is not user:

                    # If user is not None, then it must return the same user

                    raise AuthError("Internal error: "

                        "Bad authentication module (changed user)")

                if user is None:

                    # We just got ourselves some user details from an external

                    # source. Put them in the DB.

                    # TODO: Write user to DB

                    pass

                return auth_result

            else:

                raise AuthError("Internal error: "

                    "Bad authentication module (bad return type)")

        # No auths checked out; fail.

        raise AuthError()

    finally:

        dbconn.close()

def simple_db_auth(dbconn, login, password, user):

    """

    A plugin auth function, as described above.

    This one just authenticates against the local database.

    Returns None if the password in the DB is NULL, indicating that another

    auth method should be used.

    Raises an AuthError if mismatched, indicating failure to auth.

    """

    auth_result = dbconn.user_authenticate(login, password)

    # auth_result is either True, False (fail) or None (try another)

    if auth_result is None:

        return None

    elif auth_result:

        return user

    else:

        raise AuthError()

def ldap_auth(dbconn, login, password, user):

    """

    A plugin auth function, as described above.

    This one authenticates against an LDAP server.

    Returns user if successful. Raises AuthError if unsuccessful.

    Also raises AuthError if the LDAP server had an unexpected error.

    """

    try:

        l = ldap.initialize(conf.ldap_url)

        # ldap_format_string contains a "%s" to put the login name

        l.simple_bind_s(conf.ldap_format_string % login, password)

    except ldap.INVALID_CREDENTIALS:

        raise AuthError()

    except Exception, msg:

        raise AuthError("Internal error (LDAP auth): %s" % repr(msg))

    # Got here - Must have successfully authenticated with LDAP

    return user

# List of auth plugin modules, in the order to try them

auth_modules = [

    simple_db_auth,

    ldap_auth,

]