Integrating non-WP php pages and tables

I have some php-coded pages that need to be incorporated into a WP membership site – with different types of membership.

1) What is the best way just to enter raw php/html on a page? I see a number of plugins but can anyone advise which is the best?

2) How to integrate the user login with the WP membership login? I don’t want to create a separate login facility when a perfectly serviceable one already exists! In particular, I will want to intercept a plain text password before encryption (which probably means a code hack) and use the appropriate table to natural join with a table that I add to the database. One of the puzzles at the moment is that I don’t recognise what encryption WP is using but it may be that some plugins use different tables and encryptions. (starting with $P$ is not md5 or sha2 types AFAIK).