only set the Content-Type header when one hasn't already been set
only set the Content-Type header when one hasn't already been set

RangelReale/osin,helojo/osin,liggitt/osin,DejaMi/osin,ahmet/osin,airondumael/osin,observadorpt/osin,Iceyer/osin,agtorre/osin,girirajsharma/osin,jonnyreeves/osin,go-osin/osin,gpndata/osin,Inflatablewoman/osin,lancecarlson/osin,oyediyildiz/osin,hoysoft/osin,gogap/oauth2