[AIRFLOW-967] Wrap strings in native for py2 ldap compatibility

ldap3 has issues with newstr being passed. This
wraps any call
that goes over the wire to the ldap server in
native() to ensure
the native string type is used.

Closes apache#2141 from bolkedebruin/AIRFLOW-967

airflow/contrib/auth/backends/ldap_auth.py

@@ -11,6 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+from future.utils import native
 
 import flask_login
 from flask_login import login_required, current_user, logout_user
@@ -60,7 +61,7 @@ def get_ldap_connection(dn=None, password=None):
         pass
 
     server = Server(configuration.get("ldap", "uri"), use_ssl, tls_configuration)
-    conn = Connection(server, dn, password)
+    conn = Connection(server, native(dn), native(password))
 
     if not conn.bind():
         LOG.error("Cannot bind to ldap server: %s ", conn.last_error)
@@ -71,14 +72,15 @@ def get_ldap_connection(dn=None, password=None):
 
 def group_contains_user(conn, search_base, group_filter, user_name_attr, username):
     search_filter = '(&({0}))'.format(group_filter)
-    if not conn.search(search_base, search_filter, attributes=[user_name_attr]):
+    if not conn.search(native(search_base), native(search_filter),
+                       attributes=[native(user_name_attr)]):
         LOG.warning("Unable to find group for %s %s", search_base, search_filter)
     else:
         for resp in conn.response:
             if (
-                'attributes' in resp and (
-                    resp['attributes'].get(user_name_attr)[0] == username or
-                    resp['attributes'].get(user_name_attr) == username
+                        'attributes' in resp and (
+                            resp['attributes'].get(user_name_attr)[0] == username or
+                            resp['attributes'].get(user_name_attr) == username
                 )
             ):
                 return True
@@ -87,7 +89,7 @@ def group_contains_user(conn, search_base, group_filter, user_name_attr, usernam
 
 def groups_user(conn, search_base, user_filter, user_name_att, username):
     search_filter = "(&({0})({1}={2}))".format(user_filter, user_name_att, username)
-    res = conn.search(search_base, search_filter, attributes=["memberOf"])
+    res = conn.search(native(search_base), native(search_filter), attributes=[native("memberOf")])
     if not res:
         LOG.info("Cannot find user %s", username)
         raise AuthenticationError("Invalid username or password")
@@ -118,7 +120,8 @@ def __init__(self, user):
         self.ldap_groups = []
 
         # Load and cache superuser and data_profiler settings.
-        conn = get_ldap_connection(configuration.get("ldap", "bind_user"), configuration.get("ldap", "bind_password"))
+        conn = get_ldap_connection(configuration.get("ldap", "bind_user"),
+                                   configuration.get("ldap", "bind_password"))
         try:
             self.superuser = group_contains_user(conn,
                                                  configuration.get("ldap", "basedn"),
@@ -151,7 +154,8 @@ def __init__(self, user):
 
     @staticmethod
     def try_login(username, password):
-        conn = get_ldap_connection(configuration.get("ldap", "bind_user"), configuration.get("ldap", "bind_password"))
+        conn = get_ldap_connection(configuration.get("ldap", "bind_user"),
+                                   configuration.get("ldap", "bind_password"))
 
         search_filter = "(&({0})({1}={2}))".format(
             configuration.get("ldap", "user_filter"),
@@ -171,7 +175,9 @@ def try_login(username, password):
 
         # todo: BASE or ONELEVEL?
 
-        res = conn.search(configuration.get("ldap", "basedn"), search_filter, search_scope=search_scope)
+        res = conn.search(native(configuration.get("ldap", "basedn")),
+                          native(search_filter),
+                          search_scope=native(search_scope))
 
         # todo: use list or result?
         if not res: