diff --git a/packages/netlify-cms-core/index.d.ts b/packages/netlify-cms-core/index.d.ts
index 2a82e4d3..dd19bbc2 100644
--- a/packages/netlify-cms-core/index.d.ts
+++ b/packages/netlify-cms-core/index.d.ts
@@ -355,6 +355,7 @@ declare module 'netlify-cms-core' {
     site_domain?: string;
     base_url?: string;
     auth_endpoint?: string;
+    auth_type?: 'implicit' | 'pkce';
     cms_label_prefix?: string;
     squash_merges?: boolean;
     proxy_url?: string;