diff --git a/src/auth.rs b/src/auth.rs
index f8d4224..fc36db1 100644
--- a/src/auth.rs
+++ b/src/auth.rs
@@ -46,7 +46,7 @@ impl UserAuthenticator {
 
     #[instrument]
     pub async fn create_user_token(
-        &mut self,
+        &self,
         username: &str,
         password: &Password,
     ) -> Result<UserToken, AuthenticationError> {