HTTP Basic Authentication
SearchWP’s default indexing process is built upon a process that runs in the background on your server. It works by making sequential HTTP requests to itself (loopback connections) which in turn causes the indexer to build its index.
If your server has implemented HTTP Basic Authentication, you will need to provide the login information to SearchWP in order for the indexer to operate successfully. If SearchWP’s indexer cannot function due to HTTP Basic Authentication you will see this notice on the Engines tab of the SearchWP settings screen:
You will need to make use of the searchwp\background_process\http_basic_auth_credentials
hook to pass along your HTTP Basic Authentication username and password.
Once that hook is in place, the notice will disappear and SearchWP’s indexer will operate as expected.