R1:7081923bd73c

Adding 'Secure Browsing' config setting to Facebook OAuth.

Summary: The Graph API exposes a new field, security_settings, which allows applications to see whether a user has enabled Secure Browsing. This diff adds a configuration setting to Phabricator which forces users to have Secure Browsing enabled when logging in via Facebook.

Test Plan: With the configuration setting off, verify that secure browsing does not affect the ability to log in. With the configuration setting on and secure browsing off…