Curl -u equivalent in HTTP request

The easy way is adding credential into url as user:pass@ format.

https://my-secret-toggl-api-token:[email protected]/reports/api/v2/project/?page=...
        <---------------------------------->

Alternately you can use credential with your http header like below:

Authorization: Basic XXXXXX

Here XXXXXX is base64(my-secret-toggl-api-token:api_token)