If user activates a basic authentication method by clicking on it, leaves either username or password field empty and clicks the Login button, warning message will appear.

If user fills out both fields, temporary progress frame will be activated and authentication request will be sent. In case of incorrect credentials a message will be displayed and authentication frame will be activated again. In case of correct credentials current page will be updated.

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Anton: Server-side authentication code works as described and is unit testable (#539).