Auth Server and Middleware

Auth Server and Middleware

Creating Your Own Auth Server and Middleware

The included swift/common/middleware/tempauth.py is a good example of how to create an auth subsystem with proxy server auth middleware. The main points are that the auth middleware can reject requests up front, before they ever get to the Swift Proxy application, and afterwards when the proxy issues callbacks to verify authorization.

It’s generally good to separate the authentication and authorization procedures. Authentication verifies that a request actually comes from who it says it does. Authorization verifies the ‘who’ has access to the resource(s) the request wants.

Authentication is performed on the request before it ever gets to the Swift Proxy application. The identity information is gleaned from the request, validated in some way, and the validation information is added to the WSGI environment as needed by the future authorization procedure. What exactly is added to the WSGI environment is solely dependent on what the installed authorization procedures need; the Swift Proxy application itself needs no specific information, it just passes it along. Convention has environ[‘REMOTE_USER’] set to the authenticated user string but often more information is needed than just that.

The included TempAuth will set the REMOTE_USER to a comma separated list of groups the user belongs to. The first group will be the “user’s group”, a group that only the user belongs to. The second group will be the “account’s group”, a group that includes all users for that auth account (different than the storage account). The third group is optional and is the storage account string. If the user does not have admin access to the account, the third group will be omitted.

It is highly recommended that authentication server implementers prefix their tokens and Swift storage accounts they create with a configurable reseller prefix (AUTH_ by default with the included TempAuth). This prefix will avoid conflicts with other authentication servers that might be using the same Swift cluster. Otherwise, the Swift cluster will have to try all the resellers until one validates a token or all fail.

A restriction with group names is that no group name should begin with a period ‘.’ as that is reserved for internal Swift use (such as the .r for referrer designations as you’ll see later).

Example Authentication with TempAuth:

  • Token AUTH_tkabcd is given to the TempAuth middleware in a request’s X-Auth-Token header.
  • The TempAuth middleware validates the token AUTH_tkabcd and discovers it matches the “tester” user within the “test” account for the storage account “AUTH_storage_xyz”.
  • The TempAuth middleware sets the REMOTE_USER to “test:tester,test,AUTH_storage_xyz”
  • Now this user will have full access (via authorization procedures later) to the AUTH_storage_xyz Swift storage account and access to containers in other storage accounts, provided the storage account begins with the same AUTH_ reseller prefix and the container has an ACL specifying at least one of those three groups.

Authorization is performed through callbacks by the Swift Proxy server to the WSGI environment’s swift.authorize value, if one is set. The swift.authorize value should simply be a function that takes a Request as an argument and returns None if access is granted or returns a callable(environ, start_response) if access is denied. This callable is a standard WSGI callable. Generally, you should return 403 Forbidden for requests by an authenticated user and 401 Unauthorized for an unauthenticated request. For example, here’s an authorize function that only allows GETs (in this case you’d probably return 405 Method Not Allowed, but ignore that for the moment).:

from swift.common.swob import HTTPForbidden, HTTPUnauthorized


def authorize(req):
    if req.method == 'GET':
        return None
    if req.remote_user:
        return HTTPForbidden(request=req)
    else:
        return HTTPUnauthorized(request=req)

Adding the swift.authorize callback is often done by the authentication middleware as authentication and authorization are often paired together. But, you could create separate authorization middleware that simply sets the callback before passing on the request. To continue our example above:

from swift.common.swob import HTTPForbidden, HTTPUnauthorized


class Authorization(object):

    def __init__(self, app, conf):
        self.app = app
        self.conf = conf

    def __call__(self, environ, start_response):
        environ['swift.authorize'] = self.authorize
        return self.app(environ, start_response)

    def authorize(self, req):
        if req.method == 'GET':
            return None
        if req.remote_user:
            return HTTPForbidden(request=req)
        else:
            return HTTPUnauthorized(request=req)


def filter_factory(global_conf, **local_conf):
    conf = global_conf.copy()
    conf.update(local_conf)
    def auth_filter(app):
        return Authorization(app, conf)
    return auth_filter

The Swift Proxy server will call swift.authorize after some initial work, but before truly trying to process the request. Positive authorization at this point will cause the request to be fully processed immediately. A denial at this point will immediately send the denial response for most operations.

But for some operations that might be approved with more information, the additional information will be gathered and added to the WSGI environment and then swift.authorize will be called once more. These are called delay_denial requests and currently include container read requests and object read and write requests. For these requests, the read or write access control string (X-Container-Read and X-Container-Write) will be fetched and set as the ‘acl’ attribute in the Request passed to swift.authorize.

The delay_denial procedures allow skipping possibly expensive access control string retrievals for requests that can be approved without that information, such as administrator or account owner requests.

To further our example, we now will approve all requests that have the access control string set to same value as the authenticated user string. Note that you probably wouldn’t do this exactly as the access control string represents a list rather than a single user, but it’ll suffice for this example:

from swift.common.swob import HTTPForbidden, HTTPUnauthorized


class Authorization(object):

    def __init__(self, app, conf):
        self.app = app
        self.conf = conf

    def __call__(self, environ, start_response):
        environ['swift.authorize'] = self.authorize
        return self.app(environ, start_response)

    def authorize(self, req):
        # Allow anyone to perform GET requests
        if req.method == 'GET':
            return None
        # Allow any request where the acl equals the authenticated user
        if getattr(req, 'acl', None) == req.remote_user:
            return None
        if req.remote_user:
            return HTTPForbidden(request=req)
        else:
            return HTTPUnauthorized(request=req)


def filter_factory(global_conf, **local_conf):
    conf = global_conf.copy()
    conf.update(local_conf)
    def auth_filter(app):
        return Authorization(app, conf)
    return auth_filter

The access control string has a standard format included with Swift, though this can be overridden if desired. The standard format can be parsed with swift.common.middleware.acl.parse_acl which converts the string into two arrays of strings: (referrers, groups). The referrers allow comparing the request’s Referer header to control access. The groups allow comparing the request.remote_user (or other sources of group information) to control access. Checking referrer access can be accomplished by using the swift.common.middleware.acl.referrer_allowed function. Checking group access is usually a simple string comparison.

Let’s continue our example to use parse_acl and referrer_allowed. Now we’ll only allow GETs after a referrer check and any requests after a group check:

from swift.common.middleware.acl import parse_acl, referrer_allowed
from swift.common.swob import HTTPForbidden, HTTPUnauthorized


class Authorization(object):

    def __init__(self, app, conf):
        self.app = app
        self.conf = conf

    def __call__(self, environ, start_response):
        environ['swift.authorize'] = self.authorize
        return self.app(environ, start_response)

    def authorize(self, req):
        if hasattr(req, 'acl'):
            referrers, groups = parse_acl(req.acl)
            if req.method == 'GET' and referrer_allowed(req, referrers):
                return None
            if req.remote_user and groups and req.remote_user in groups:
                return None
        if req.remote_user:
            return HTTPForbidden(request=req)
        else:
            return HTTPUnauthorized(request=req)


def filter_factory(global_conf, **local_conf):
    conf = global_conf.copy()
    conf.update(local_conf)
    def auth_filter(app):
        return Authorization(app, conf)
    return auth_filter

The access control strings are set with PUTs and POSTs to containers with the X-Container-Read and X-Container-Write headers. Swift allows these strings to be set to any value, though it’s very useful to validate that the strings meet the desired format and return a useful error to the user if they don’t.

To support this validation, the Swift Proxy application will call the WSGI environment’s swift.clean_acl callback whenever one of these headers is to be written. The callback should take a header name and value as its arguments. It should return the cleaned value to save if valid or raise a ValueError with a reasonable error message if not.

There is an included swift.common.middleware.acl.clean_acl that validates the standard Swift format. Let’s improve our example by making use of that:

from swift.common.middleware.acl import \
    clean_acl, parse_acl, referrer_allowed
from swift.common.swob import HTTPForbidden, HTTPUnauthorized


class Authorization(object):

    def __init__(self, app, conf):
        self.app = app
        self.conf = conf

    def __call__(self, environ, start_response):
        environ['swift.authorize'] = self.authorize
        environ['swift.clean_acl'] = clean_acl
        return self.app(environ, start_response)

    def authorize(self, req):
        if hasattr(req, 'acl'):
            referrers, groups = parse_acl(req.acl)
            if req.method == 'GET' and referrer_allowed(req, referrers):
                return None
            if req.remote_user and groups and req.remote_user in groups:
                return None
        if req.remote_user:
            return HTTPForbidden(request=req)
        else:
            return HTTPUnauthorized(request=req)


def filter_factory(global_conf, **local_conf):
    conf = global_conf.copy()
    conf.update(local_conf)
    def auth_filter(app):
        return Authorization(app, conf)
    return auth_filter

Now, if you want to override the format for access control strings you’ll have to provide your own clean_acl function and you’ll have to do your own parsing and authorization checking for that format. It’s highly recommended you use the standard format simply to support the widest range of external tools, but sometimes that’s less important than meeting certain ACL requirements.

Integrating With repoze.what

Here’s an example of integration with repoze.what, though honestly I’m no repoze.what expert by any stretch; this is just included here to hopefully give folks a start on their own code if they want to use repoze.what:

from time import time

from eventlet.timeout import Timeout
from repoze.what.adapters import BaseSourceAdapter
from repoze.what.middleware import setup_auth
from repoze.what.predicates import in_any_group, NotAuthorizedError
from swift.common.bufferedhttp import http_connect_raw as http_connect
from swift.common.middleware.acl import clean_acl, parse_acl, referrer_allowed
from swift.common.utils import cache_from_env, split_path
from swift.common.swob import HTTPForbidden, HTTPUnauthorized


class DevAuthorization(object):

    def __init__(self, app, conf):
        self.app = app
        self.conf = conf

    def __call__(self, environ, start_response):
        environ['swift.authorize'] = self.authorize
        environ['swift.clean_acl'] = clean_acl
        return self.app(environ, start_response)

    def authorize(self, req):
        version, account, container, obj = split_path(req.path, 1, 4, True)
        if not account:
            return self.denied_response(req)
        referrers, groups = parse_acl(getattr(req, 'acl', None))
        if referrer_allowed(req, referrers):
            return None
        try:
            in_any_group(account, *groups).check_authorization(req.environ)
        except NotAuthorizedError:
            return self.denied_response(req)
        return None

    def denied_response(self, req):
        if req.remote_user:
            return HTTPForbidden(request=req)
        else:
            return HTTPUnauthorized(request=req)


class DevIdentifier(object):

    def __init__(self, conf):
        self.conf = conf

    def identify(self, env):
        return {'token':
                env.get('HTTP_X_AUTH_TOKEN', env.get('HTTP_X_STORAGE_TOKEN'))}

    def remember(self, env, identity):
        return []

    def forget(self, env, identity):
        return []


class DevAuthenticator(object):

    def __init__(self, conf):
        self.conf = conf
        self.auth_host = conf.get('ip', '127.0.0.1')
        self.auth_port = int(conf.get('port', 11000))
        self.ssl = \
            conf.get('ssl', 'false').lower() in ('true', 'on', '1', 'yes')
        self.auth_prefix = conf.get('prefix', '/')
        self.timeout = float(conf.get('node_timeout', 10))

    def authenticate(self, env, identity):
        token = identity.get('token')
        if not token:
            return None
        memcache_client = cache_from_env(env)
        key = 'devauth/%s' % token
        cached_auth_data = memcache_client.get(key)
        if cached_auth_data:
            start, expiration, user = cached_auth_data
            if time() - start <= expiration:
                return user
        with Timeout(self.timeout):
            conn = http_connect(self.auth_host, self.auth_port, 'GET',
                    '%stoken/%s' % (self.auth_prefix, token), ssl=self.ssl)
            resp = conn.getresponse()
            resp.read()
            conn.close()
        if resp.status == 204:
            expiration = float(resp.getheader('x-auth-ttl'))
            user = resp.getheader('x-auth-user')
            memcache_client.set(key, (time(), expiration, user),
                                time=expiration)
            return user
        return None


class DevChallenger(object):

    def __init__(self, conf):
        self.conf = conf

    def challenge(self, env, status, app_headers, forget_headers):
        def no_challenge(env, start_response):
            start_response(str(status), [])
            return []
        return no_challenge


class DevGroupSourceAdapter(BaseSourceAdapter):

    def __init__(self, *args, **kwargs):
        super(DevGroupSourceAdapter, self).__init__(*args, **kwargs)
        self.sections = {}

    def _get_all_sections(self):
        return self.sections

    def _get_section_items(self, section):
        return self.sections[section]

    def _find_sections(self, credentials):
        return credentials['repoze.what.userid'].split(',')

    def _include_items(self, section, items):
        self.sections[section] |= items

    def _exclude_items(self, section, items):
        for item in items:
            self.sections[section].remove(item)

    def _item_is_included(self, section, item):
        return item in self.sections[section]

    def _create_section(self, section):
        self.sections[section] = set()

    def _edit_section(self, section, new_section):
        self.sections[new_section] = self.sections[section]
        del self.sections[section]

    def _delete_section(self, section):
        del self.sections[section]

    def _section_exists(self, section):
        return self.sections.has_key(section)


class DevPermissionSourceAdapter(BaseSourceAdapter):

    def __init__(self, *args, **kwargs):
        super(DevPermissionSourceAdapter, self).__init__(*args, **kwargs)
        self.sections = {}

    def _get_all_sections(self):
        return self.sections

    def _get_section_items(self, section):
        return self.sections[section]

    def _find_sections(self, group_name):
        return set([n for (n, p) in self.sections.items()
                    if group_name in p])

    def _include_items(self, section, items):
        self.sections[section] |= items

    def _exclude_items(self, section, items):
        for item in items:
            self.sections[section].remove(item)

    def _item_is_included(self, section, item):
        return item in self.sections[section]

    def _create_section(self, section):
        self.sections[section] = set()

    def _edit_section(self, section, new_section):
        self.sections[new_section] = self.sections[section]
        del self.sections[section]

    def _delete_section(self, section):
        del self.sections[section]

    def _section_exists(self, section):
        return self.sections.has_key(section)


def filter_factory(global_conf, **local_conf):
    conf = global_conf.copy()
    conf.update(local_conf)
    def auth_filter(app):
        return setup_auth(DevAuthorization(app, conf),
            group_adapters={'all_groups': DevGroupSourceAdapter()},
            permission_adapters={'all_perms': DevPermissionSourceAdapter()},
            identifiers=[('devauth', DevIdentifier(conf))],
            authenticators=[('devauth', DevAuthenticator(conf))],
            challengers=[('devauth', DevChallenger(conf))])
    return auth_filter

Allowing CORS with Auth

Cross Origin Resource Sharing (CORS) require that the auth system allow the OPTIONS method to pass through without a token. The preflight request will make an OPTIONS call against the object or container and will not work if the auth system stops it. See TempAuth for an example of how OPTIONS requests are handled.

Creative Commons Attribution 3.0 License

Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License. See all OpenStack Legal Documents.

swift 2.19.1.dev121