[#23] Wrote test for Digest identity retrieval

- Mock HTTP auth adapter returns a Result object with an identity
  composed such as Digest authentication would return; test case
  indicates we should retrieve the discovered username; assertion
  currently fails.
[#23] Inject role name based on username in identity

- If an array is present for the identity, and it contains a "username"
  property, use that for the role name. If it does not, cast the array
  to a string.
Merge branch 'weierophinney-hotfix/23'

* weierophinney-hotfix/23:
  [#23] Inject role name based on username in identity
  [#23] Wrote test for Digest identity retrieval