This happens when we upgrade my Apache to 2.4.7 , it turns out that we haven’t got removed the old authentication configuration completely, we just remove the require valid user
#AuthType Basic AuthName "My Login" AuthUserFile /var/www/.htpasswd #Require valid-user
The fix is: we have to remove all authentication configuration lines
#AuthType Basic #AuthName "My Login" #AuthUserFile /var/www/.htpasswd #Require valid-user