One password, one page, many users

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Hello,
I'm putting together a site for a company - I'm not a PHP developer - strictly front end so I'm hoping I can sort this with the C5 interface and page permissions.
They want to assign a single password to many of their customers. All use the same password to access one page on the site which is invisible to anyone who isn't logged in with the password.
Do members have to have unique passwords? Will it cause problems on the site if a few people are logged in at the same time with the same password?
Thanks
Allison

mexicanred