Missing decode on client basic authentication

[strehle]

see cloudfoundry/uaa#778

The RFC for OAuth requires an URL encode in authorization header, see
https://tools.ietf.org/html/rfc6749#section-2.3

The authorization header needs to be
Authorization: Basic base64Encode(urlencode(client_id):urlencode(client_secret))

UAAC does not encode the authorization header. (client)
UAA does not decode the authorization header (server)
Thus this issue does popup in uaac before, however uaac should behave standard conform.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/155510328

The labels on this github issue will be updated when the story is started.