Couchbase or Sync Gateway

[atom_yang]

@danthi

use Couchbase directly on port 8092, or if it should also leverage Sync Gateway for accessing data.

if you use sync gateway 1.5 or higher, you can use Couchbase directly by enable XATTRs. FYI

@danthi

What are the pros/cons for each method

if you enable XATTRs, the changed from Couchbase directly will trigger the channel allocation with sync gateway, and you can use N1QL to get/update document. but it will ignore the require* function .
FYI and this

@danthi

if the web app uses Couchbase is there an authentication mechanism to authenticate the app other than the External Users/Roles?

Couchbase server only store user info, if you want to your app and web the same user certificate, you should use Sync Gateway authentication mechanism . you can Custom Authentication with this guide.