When prompted for the credentials when the JNLP is downloaded, did you try typing in the admin credentials ?
I have the same issue. Rather than downloading the jnlp, I created a .bat script to access from http://***/cmx/siperian-console.jnlp.
My question is Why is it asking for credentials while downloading the jnlp?
MDM Version- 10.2 HF2.
10.3 HF1 is still not released.
Can you confirm your exact version?
From MDM 10.2 HF2 version, JNLP is maintained at session level so giving username and password is mandatory to use it.
As explained in above comment, JNLP is now maintained at session level.
Once you log out of MDM hub console, you have to launch it again and previous JNLP will become invalid.
This is a new feature added for enhanced security.