[refactor] token verification moved to couch module + tests

Added tests for this token verification as it wasn't covered. Then moved
it to the new couch module that implements a couch storage.
The ServerState was chosen to hold the verify_token method.
CouchServerState holds the current implementation, which is called on
authentication middleware as the new test shows.

2 files changed, 77 insertions, 0 deletions

diff --git a/common/src/leap/soledad/common/couch/state.py b/common/src/leap/soledad/common/couch/state.py
index 39d49fa0..40c0d55b 100644
--- a/common/src/leap/soledad/common/couch/state.py
+++ b/common/src/leap/soledad/common/couch/state.py
@@ -19,11 +19,14 @@ Server state using CouchDatabase as backend.
 """
 import re
 import logging
+import time
 from urlparse import urljoin
+from hashlib import sha512
 
 from u1db.remote.server_state import ServerState
 from leap.soledad.common.command import exec_validated_cmd
 from leap.soledad.common.couch import CouchDatabase
+from leap.soledad.common.couch import couch_server
 from u1db.errors import Unauthorized
 
 
@@ -50,6 +53,12 @@ class CouchServerState(ServerState):
     Inteface of the WSGI server with the CouchDB backend.
     """
 
+    TOKENS_DB_PREFIX = "tokens_"
+    TOKENS_DB_EXPIRE = 30 * 24 * 3600  # 30 days in seconds
+    TOKENS_TYPE_KEY = "type"
+    TOKENS_TYPE_DEF = "Token"
+    TOKENS_USER_ID_KEY = "user_id"
+
     def __init__(self, couch_url, create_cmd=None):
         """
         Initialize the couch server state.
@@ -112,3 +121,40 @@ class CouchServerState(ServerState):
                              delete databases.
         """
         raise Unauthorized()
+
+    def verify_token(self, uuid, token):
+        """
+        Query couchdb to decide if C{token} is valid for C{uuid}.
+
+        @param uuid: The user uuid.
+        @type uuid: str
+        @param token: The token.
+        @type token: str
+        """
+        with couch_server(self.couch_url) as server:
+            # the tokens db rotates every 30 days, and the current db name is
+            # "tokens_NNN", where NNN is the number of seconds since epoch divided
+            # by the rotate period in seconds. When rotating, old and new tokens
+            # db coexist during a certain window of time and valid tokens are
+            # replicated from the old db to the new one. See:
+            # https://leap.se/code/issues/6785
+            dbname = self._tokens_dbname()
+            db = server[dbname]
+        # lookup key is a hash of the token to prevent timing attacks.
+        token = db.get(sha512(token).hexdigest())
+        if token is None:
+            return False
+        # we compare uuid hashes to avoid possible timing attacks that
+        # might exploit python's builtin comparison operator behaviour,
+        # which fails immediatelly when non-matching bytes are found.
+        couch_uuid_hash = sha512(token[self.TOKENS_USER_ID_KEY]).digest()
+        req_uuid_hash = sha512(uuid).digest()
+        if token[self.TOKENS_TYPE_KEY] != self.TOKENS_TYPE_DEF \
+                or couch_uuid_hash != req_uuid_hash:
+            return False
+        return True
+
+    def _tokens_dbname(self):
+        dbname = self.TOKENS_DB_PREFIX + \
+            str(int(time.time() / self.TOKENS_DB_EXPIRE))
+        return dbname
diff --git a/common/src/leap/soledad/common/tests/test_server.py b/common/src/leap/soledad/common/tests/test_server.py
index d75275d6..e1129a9f 100644
--- a/common/src/leap/soledad/common/tests/test_server.py
+++ b/common/src/leap/soledad/common/tests/test_server.py
@@ -24,6 +24,7 @@ import time
 import binascii
 from pkg_resources import resource_filename
 from uuid import uuid4
+from hashlib import sha512
 
 from urlparse import urljoin
 from twisted.internet import defer
@@ -46,6 +47,36 @@ from leap.soledad.server import LockResource
 from leap.soledad.server import load_configuration
 from leap.soledad.server import CONFIG_DEFAULTS
 from leap.soledad.server.auth import URLToAuthorization
+from leap.soledad.server.auth import SoledadTokenAuthMiddleware
+
+
+class ServerAuthenticationMiddlewareTestCase(CouchDBTestCase):
+
+    def setUp(self):
+        super(ServerAuthenticationMiddlewareTestCase, self).setUp()
+        app = mock.Mock()
+        self._state = CouchServerState(self.couch_url)
+        app.state = self._state
+        self.auth_middleware = SoledadTokenAuthMiddleware(app)
+        self._authorize('valid-uuid', 'valid-token')
+
+    def _authorize(self, uuid, token):
+        token_doc = {}
+        token_doc['_id'] = sha512(token).hexdigest()
+        token_doc[self._state.TOKENS_USER_ID_KEY] = uuid
+        token_doc[self._state.TOKENS_TYPE_KEY] = \
+            self._state.TOKENS_TYPE_DEF
+        dbname = self._state._tokens_dbname()
+        db = self.couch_server.create(dbname)
+        db.save(token_doc)
+        self.addCleanup(self.delete_db, db.name)
+
+    def test_authorized_user(self):
+        is_authorized = self.auth_middleware._verify_authentication_data
+        self.assertTrue(is_authorized('valid-uuid', 'valid-token'))
+        self.assertFalse(is_authorized('valid-uuid', 'invalid-token'))
+        self.assertFalse(is_authorized('invalid-uuid', 'valid-token'))
+        self.assertFalse(is_authorized('eve', 'invalid-token'))
 
 
 class ServerAuthorizationTestCase(BaseSoledadTest):