* caddyauth: Add singleflight for basic auth
* Fixes#5338
* it occurred the thunder herd problem like this https://medium.com/@mhrlife/avoid-duplicate-requests-while-filling-cache-98c687879f59
* Update modules/caddyhttp/caddyauth/basicauth.go
Fix comment
Co-authored-by: Francis Lavoie <lavofr@gmail.com>
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Co-authored-by: Francis Lavoie <lavofr@gmail.com>
Co-authored-by: Matt Holt <mholt@users.noreply.github.com>