finall ldap support

migrations/postgres/0013_directory_identity.sql

@@ -0,0 +1,4 @@
+ALTER TABLE users ADD COLUMN auth_provider TEXT NOT NULL DEFAULT 'local';
+ALTER TABLE users ADD COLUMN external_id TEXT;
+ALTER TABLE users ADD COLUMN external_dn TEXT;
+CREATE UNIQUE INDEX idx_users_external_identity ON users(auth_provider, external_id) WHERE external_id IS NOT NULL;