Expose ldap pool active parameter to limit retries

Currently the pool is initiated so that servers are retried
indefinetely. This makes it hard to define concrete hard timeout for
login operation.

This change exposes ldap3's ServerPool active parameter as setting. That
way it provides means to resolve situations as with etianen#264.

https://ldap3.readthedocs.io/en/latest/server.html#server-pool

README.rst

@@ -94,6 +94,8 @@ Available settings
     LDAP_AUTH_CONNECT_TIMEOUT = None
     LDAP_AUTH_RECEIVE_TIMEOUT = None
 
+    # Set connection pool `active` parameter on the underlying `ldap3` library.
+    LDAP_AUTH_POOL_ACTIVE = True
 
 Microsoft Active Directory support
 ----------------------------------

django_python3_ldap/conf.py

@@ -136,5 +136,10 @@ def __init__(self, settings):
         default=None
     )
 
+    LDAP_AUTH_POOL_ACTIVE = LazySetting(
+        name="LDAP_AUTH_POOL_ACTIVE",
+        default=True
+    )
+
 
 settings = LazySettings(settings)

django_python3_ldap/ldap.py

@@ -162,7 +162,11 @@ def connection(**kwargs):
         password = kwargs.pop("password")
         username = format_username(kwargs)
     # Build server pool
-    server_pool = ldap3.ServerPool(None, ldap3.RANDOM, active=True, exhaust=5)
+    server_pool = ldap3.ServerPool(
+        None, ldap3.RANDOM,
+        active=settings.LDAP_AUTH_POOL_ACTIVE,
+        exhaust=5
+    )
     auth_url = settings.LDAP_AUTH_URL
     if not isinstance(auth_url, list):
         auth_url = [auth_url]

django_python3_ldap/tests.py

@@ -149,6 +149,18 @@ def testAuthenticateWithFailedRebind(self):
             )
             self.assertIs(user, None)
 
+    def testAuthenticateWithLimitedRetries(self):
+        # simulate offline server
+        with self.settings(
+            LDAP_AUTH_URL=["ldap://example.com:389"],
+            LDAP_AUTH_POOL_ACTIVE=1,
+        ):
+            user = authenticate(
+                username=settings.LDAP_AUTH_TEST_USER_USERNAME,
+                password=settings.LDAP_AUTH_TEST_USER_PASSWORD,
+            )
+        self.assertEqual(user, None)
+
     # User synchronisation.
 
     def testSyncUsersCreatesUsers(self):