Merge branch 'preauth-test' into 'master'

Test all the things!

This merge request improves the code coverage of the project's unit tests.

I broke up this rather large set of changes into separate commits. See the individual commit messages for details.

* 75773b6d - Use PHPUnit provided by Composer instead of downloading a PHAR
* 737771f2 - Convert dashes to underscores when converting to HTTP headers
* 08aaa966 - Group conditional logic for clarity
* 1477621c - Create missing tests for PreauthUserDetailsProvider, introduce an EnvironmentHelper
* b74fd618 - Federated preauth tests made consistent with new preauth tests, improved coverage, moved test data from JSON to source code
* 09d36d36 - LocalUserDetailsProvider throws Exception if JSON is invalid, returns null if JSON is missing
* d021fd72 - Verify missing attributes are set as false
* e29430a9 - Docblock and PSR-2 formatting improvements

### PHP Trait

In 1477621c, I introduced a lesser-known feature of PHP called a [trait](http://php.net/manual/en/language.oop5.traits.php). It allows one to "inject" common methods into any class without requiring inheritance.

@andrew-summers @weizhong-wang @KJOYNER

See merge request !12