Testing HTTP connections and Rest APIs can easily be done using Postman. This handy tool allows you to provide HTTP headers, among many other things, to test connections and view responses.
Here’s a test of querying a Rest API from restdb.io. The query URL is https://testdb-cd69.restdb.io/rest/people. For authentication, an HTTP header called “x-apikey” is provided with its value (redacted). The response from the call is in the body panel in JSON format.