How to pass the authentication credentials?

I am trying to make an api request to get images.
But I am confused how to pass my api credentials.Please help me with it.In python based doc section the api key is passed as plotly_private,but in curl it is username:api_key.I’ve tried both but not getting response.Getting message as you must be authenticated to get images.But as per the doc api_key is enough as it follows only basic authentication.But why it’s not showing up.One more doubt is passing Plotly-Client-Platform header,what if I am using some language that is not listed there say ruby or something.Can I leave without passing it.Please help me with it.
My doubt is how the api_key should be passed whether as api_key query string or plotly_private query string params or username,api_key form data.