I have multiple websites with one master site. Is it possible that used register and login using a single username and password on all the sites. the installations are not wordpress multisite,each site is a individual website.
this is very possible.
I've done this in the past if they are in the same table but with the different extensions: (if they aren't then you can merge the 2 tables)
blog 1 (table prefix is ba1_) blog 2 (table prefix is bb2_)
so you you would have 2 user tables in your database: ba1_users bb2_users
In your wp-config of the 2nd blog: find this line:
/* That's all, stop editing! Happy blogging. */
Just above it, add:
define('CUSTOM_USER_TABLE', 'ba1_users'); define('CUSTOM_USER_META_TABLE', 'ba1_usermeta');
now blog 2 which was using bb2_users and bb2_usermeta will now use ba1_users and ba1_usermeta.
I haven't fully explored all considerations but this worked really well for me.