NPR Show a web-based login/signup form to a user

If the parameters passed to this endpoint are correct, it will redirect to `npr.org/oauth2/login` for the user to complete the sign-in. Currently acceptable values for `scope` are any combination of the following: - `identity.readonly` - for read-only access to the Identity Service - `identity.write` - for write access to the Identity Service - `listening.readonly` - for read-only access to the Listening Service - `listening.write` - for write access to the Listening Service - `localactivati...