Odd message saying "authentication required"

Mustard

Bionic Poster
Tonight, when I click on my alerts, I get a message saying something like "authentication required" and says that 80s-tennis.com is requesting my username and password and that it won't be sent to the website that I'm currently visiting. It looks like some sort of security leak on the Talk Tennis forum.

I can still carry on using the Talk Tennis forum normally despite this by clicking on the X in the top right hand corner, but these "authentication required" messages I get after clicking on an alert are strange. Will a forum moderator please look into it.
 
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