Add support for multiple ad hosts

auth.py

@@ -155,8 +155,16 @@ try:
             if ca_cert is not None:
                 tls_config = ldap3.Tls(
                     validate=ssl.CERT_REQUIRED, ca_certs_file=ca_cert)
-            self.server = ldap3.Server(
-                host, port=port, use_ssl=use_ssl, tls=tls_config)
+            if isinstance(host, str):
+                self.server = ldap3.Server(
+                    host, port=port, use_ssl=use_ssl, tls=tls_config)
+            else:
+                hosts = host
+                self.server = ldap3.ServerPool([
+                    ldap3.Server(
+                        host, port=port, use_ssl=use_ssl, tls=tls_config)
+                    for host in hosts
+                ], ldap3.FIRST)
             self.domain = domain
             self.user_dn = user_dn
             self.group_dn = group_dn