test for invalid type ofprivate_key instance
test for invalid type ofprivate_key instance

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