Thank you for the prompt reply! I searched for hours but apparently missed those posts.
I edited the /opt/bitnami/apps/wordpress/htdocs/wp-config.php file to add the 4 lines and restarted apache. I added the 4 lines plus the two REM lines above the line which says: "/* That's all, stop editing! Happy blogging. */"
I now get no login box and instead get the message: "The constant "COOKIE_DOMAIN" is defined (probably in wp-config.php). Please remove or comment out that define() line."
I get this same message at for maindomain.com, maindomain.com/wp-admin, differentdomain.com, differentdomain.com/wp-admin and the same domains with the www prefix.