Issue by @stephenheron: client credentials still added to body
Issue by @stephenheron: client credentials still added to body

See https://github.com/commerceguys/guzzle-oauth2-plugin/issues/17#issuecomment-99012595

lemasson-h/guzzle-oauth2-plugin,frankkessler/guzzle-oauth2-plugin,pjcdawkins/guzzle-oauth2-plugin,commerceguys/guzzle-oauth2-plugin,xleliberty/guzzle-oauth2-plugin,mtdavidson/guzzle-oauth2-plugin,Sainsburys/guzzle-oauth2-plugin,rampmaster/guzzle-oauth2-plugin