Use Bearer authentication

[tomasr78]

Change query authentication to bearer authentication.

curl -X GET https://v2.convertapi.com/user -H 'Authorization: Bearer secret_or_token'

[tomasr78]

The property that accepts the secret is convertapi.api_secret = 'xxxxxx'. I suggest renaming it to api_credentials because it will match the idea that a secret or token is accepted and not only a secret.

[laurynas-convertapi]

Released in version https://github.com/ConvertAPI/convertapi-library-python/releases/tag/v2.0.0