Config backend for cloud proxy with basic auth

Help!
1

Hi

I need to configure installed haproxy as a forward proxy to be able to make requests to cloud proxy which requires basic authentication

to be able to
curl -x http://my-local-ha-proxy:8000 http://example.com
without passing login:pass every time

2 
backend main
    http-request set-header Authorization Basic\ <base_64 of 'user:pass'>
3 
backend some_backend
       http-request set-header proxy-authorization Basic\ <base_64 of 'user:pass'>