auth: Fix handling passdbs with identical driver/args but different
mechanisms/username_filter
7bad6a24160e34bce8f10e73dbbf9e5fbbcd1904

Index: src/auth/auth.c
--- src/auth/auth.c.orig
+++ src/auth/auth.c
@@ -93,6 +93,24 @@ auth_passdb_preinit(struct auth *auth, const struct au
 	auth_passdb->override_fields_tmpl =
 		passdb_template_build(auth->pool, set->override_fields);
 
+	if (*set->mechanisms == '\0') {
+		auth_passdb->mechanisms = NULL;
+	} else if (strcasecmp(set->mechanisms, "none") == 0) {
+		auth_passdb->mechanisms = (const char *const[]){ NULL };
+	} else {
+		auth_passdb->mechanisms =
+			(const char *const *)p_strsplit_spaces(auth->pool,
+				set->mechanisms, " ,");
+	}
+
+	if (*set->username_filter == '\0') {
+		auth_passdb->username_filter = NULL;
+	} else {
+		auth_passdb->username_filter =
+			(const char *const *)p_strsplit_spaces(auth->pool,
+				set->username_filter, " ,");
+	}
+
 	/* for backwards compatibility: */
 	if (set->pass)
 		auth_passdb->result_success = AUTH_DB_RULE_CONTINUE;