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# Source code for authpam

    # -*- coding: utf-8 -*-
    #
    #       Copyright 2011 Liftoff Software Corporation
    #
    #   Thanks to Alan Schmitz for contributing this module!

    # Meta
    __version__ = '1.0'
    __license__ = "AGPLv3 or Proprietary (see LICENSE.txt)"
    __version_info__ = (1, 0)
    __doc__ = """
    This authentication module is built on top of python-pam (or PAM).  The latest
    version of which can be found here:  ftp://ftp.pangalactic.org/pub/tummy/ or if
    that doesn't work try:  http://packages.debian.org/lenny/python-pam

    It was originally written by Alan Schmitz.

    The only non-obvious aspect of this module is that the pam_realm setting is only
    used when the user is asked to authenticate and when the user's information is
    stored in the 'users' directory.  It isn't actually used in any part of the
    authentication (PAM doesn't take a "realm" setting).
    """

    # Standard library modules
    import base64

    # 3rd party modules
    import PAM
    import tornado.httpserver
    import tornado.ioloop
    import tornado.web

    class PAMAuthMixin(tornado.web.RequestHandler):
        """
        This is used by PAMAuthHandler in auth.py to authenticate users via PAM.
        """
        def initialize(self):
            """
            Print out helpful error messages if the requisite settings aren't
            configured.
            """
            self.require_setting("pam_realm", "PAM Realm")
            self.require_setting("pam_service", "PAM Service")

        def get_authenticated_user(self, callback):
            """
            Processes the client's Authorization header and call self.auth_basic()
            """
            auth_header = self.request.headers.get('Authorization')
            if auth_header and auth_header.startswith('Basic '):
                self.auth_basic(auth_header, callback)

        def auth_basic(self, auth_header, callback):
            """
            Perform Basic authentication using self.settings['pam_realm'].
            """
            auth_decoded = base64.decodestring(auth_header[6:])
            username, password = auth_decoded.split(':', 2)

            def _pam_conv(auth, query_list, user_data=None):
                resp = []
                for i in range(len(query_list)):
                    query, qtype = query_list[i]
                    if qtype == PAM.PAM_PROMPT_ECHO_ON:
                        resp.append((username, 0))
                    elif qtype == PAM.PAM_PROMPT_ECHO_OFF:
                        resp.append((password, 0))
                    else:
                        return None
                return resp

            pam_auth = PAM.pam()
            pam_auth.start(self.settings['pam_service'])
            pam_auth.set_item(PAM.PAM_USER, username)
            pam_auth.set_item(PAM.PAM_TTY, 'console')
            pam_auth.set_item(PAM.PAM_CONV, _pam_conv)
            try:
                pam_auth.authenticate()
                pam_auth.acct_mgmt()
            except Exception as e: # Basic auth failed
                if self.settings['debug']:
                    print(e) # Very useful for debugging Kerberos errors
                return self.authenticate_redirect()
            # NOTE: Basic auth just gives us the username without the @REALM part
            #       so we have to add it:
            user = "%s@%s" % (username, self.settings['pam_realm'])
            callback(user)

        def authenticate_redirect(self):
            """
            Informs the browser that this resource requires authentication (status
            code 401) which should prompt the browser to reply with credentials.

            The browser will be informed that we support Basic auth.
            """
            if self._headers_written:
                raise Exception('Headers have already been written')
            self.set_status(401)
            self.add_header(
                "WWW-Authenticate",
                'Basic realm="%s"' % self.settings['pam_realm']
            )
            self.finish()
            return False

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