Go through db pinning after successful shared secret auth (bug 951946)

We weren't pinning properly everytime (when you first go through the
db pinning middleware, it's too early, you aren't authenticated yet,
so we don't pin you), this might explain weird bugs after actions,
such as collection re-ordering issues...
Merge pull request #1583 from diox/fix-sharedauth-pinning

Go through db pinning after successful shared secret auth (bug 951946)