Add site access options for increased viewing permission granularity

Problem Description

Currently, Library utilizes domains to control who can access the site. However, this prohibits access on a person-by-person basis and increases the amount of maintenance needed when different aliases of the same domain are often used (ex: student@u.northwestern.edu versus student@northwestern.edu).

Feature

To address these issues, Library should support:

• individual email address access via an environment variable and OAuth configuration
• the use of regex for domain matching

Additional Information

Library accesses a user's email domain via the user's passport session and checks it against the APPROVED_DOMAINS config var.