A normal client-server transaction can follow two scenarios of basic authentication. On one hand, a client submits a request to the server without any authentication credentials (as depicted in the previous sequence diagram). On the other hand, a client submits a request to the server with the authentication credentials. Let's take a closer look at these two scenarios.
When a client submits a request without the authentication credentials, the server responds back stating unauthorized access with an HTTP error code of 401. If the request is executed from a web browser, users see the ubiquitous Authentication Required browser popup, as shown here:
Users can then supply the valid credentials ...
