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Membership portal that can use existing membership numbers

Hi, I know that a membership feature is discussed a lot here and that there are several integrations available but does anyone know if there is one that can talk to servers to fetch and recognise unique membership codes?
Someone’s floated the idea to me of moving a companies existing membership online, all the membership details are stored on a server so I was wondering if it would be possible to create a log in system where members use their existing membership number to log in and the server can identify and permit the sign up at the companies end?