The Basic Authorization assertion checks whether you use the basic authorization.
The assertion is available only in security tests. Use this assertion with the Weak Authentication security scan.
Follow these steps:

Open a security test.
Click Response Assertion next to the Weak Authentication scan.
Click
in the Assertions panel
In the New Assertions dialog, search for the Basic Authorization assertion or select it manually in the Security category.
Add more assertions to ensure the security of the tested service: