debug parameter

Hi guys,

I am trying to make this work and facing response status code 401. 

What could help me is option to allow "debug" and see plain http requests in console, including Bearer.

Support build-in log level error can be an option:
```tf
TF_LOG=ERROR terraform apply
```

EDIT: When I send api token empty, it behaves the same. What about to thrown specific error for this case? 