It is generally not recommended to add sensitive files, such as the "BingSiteAuth.xml" file, to publicly accessible web directories. The "BingSiteAuth.xml" file is used for site verification purposes with Bing Webmaster Tools, and it contains a verification code that proves ownership of the website to Bing.
Making this file publicly accessible can potentially expose your verification code and compromise the security and ownership of your website. It is best to keep sensitive files like this in a secure location and not expose them to the public.
If you need to verify your website with Bing Webmaster Tools, it is advisable to follow the recommended methods provided by Bing, which typically involve adding a verification meta tag or uploading a verification file to a specific location on your website that is not publicly accessible. This way, you can maintain the security of your website while still verifying ownership with Bing.