How to Enable Basic Authentication (user& password) to apache airflow(2.8.1) API

Question

I was trying to authenticate airflow API using user:password but getting following error.

error { "detail": null, "status": 403, "title": "Forbidden", "type": "https://airflow.apache.org/docs/apache-airflow/2.8.1/stable-rest-api-ref.html#section/Errors/PermissionDenied" }

our airflow webUI authentication is enabled is based on FAB, but i would like to enable API authentication based on user & password.

I've made change to airflow.cfg and created testuser from CLI, but still API is throwing above error.

 webserver:        
        auth_backend: airflow.contrib.auth.backends.password_auth
        authenticate: True
 api:
        auth_backends: airflow.api.auth.backend.default,airflow.api.auth.backend.basic_auth

Please suggest possible fixes ?