How to avoid urlencoding of message body set with setcontentstring in peoplesoft integration broker?

I am trying to invoke azure AD's token API to get the OAuth token. I was able to set the content-type header to application/x-www-form-urlencoded. However, when I set the content of the message body using setcontentstring() method, the whole content is getting url encoded and all the key value pairs are lost. I found this by checking the msglog.html file.

msg.SetContentString("grant_type=client_credentials&client_id=myclientidvalue&client_secret=myclientsecretvalue&resource=https://myresource.azurewebsites.net");

It get changed as below:

grant_type%3Dclient_credentials%26client_id%3Dmyclientidvalue%26client_secret%3Dmyclientsecretvalue%26resource%3Dhttps%3A%2F%2Fmyresource.azurewebsites.net