Microsoft Login azuread-oauth2 header

[fauziasf]

i'm trying to hit API '/oauth2/exchange_access_token/azuread-oauth2/' with different headers
currently the header of the 'Content-Type' = 'application/x-www-form-urlencoded'
i need to change it to 'Content-Type' = 'application/json'
i tried to add the code
builder.addHeader("Content-Type", "application/json");
in the OauthHeaderRequestInterceptor.java at line 35 butt the headers still 'Content-Type' = 'application/x-www-form-urlencoded' when i tried to inspect it in profiler
can you help me?