diff --git a/k8s/apps/matrix/external-secrets.yaml b/k8s/apps/matrix/external-secrets.yaml
index 2738904..c5b4007 100644
--- a/k8s/apps/matrix/external-secrets.yaml
+++ b/k8s/apps/matrix/external-secrets.yaml
@@ -57,6 +57,7 @@ spec:
                 issuer: https://idm.hexor.cy/application/o/matrix/
                 client_id: "{{ .oauth_client_id }}"
                 client_secret: "{{ .oauth_client_secret }}"
+                token_endpoint_auth_method: client_secret_post
                 scope: "openid profile email"
                 claims_imports:
                   localpart: