Check a user's password with DDP

I have two apps. First one is a client and the second one is the meteor app.
The first app is able to login in the meteor server via ddp using this call:

Method(‘login’, Params, CallBack)

Now, for a special security reason, I need the first app to be able to check if account password is correct (please notice that user is already logged in and I’m asking him to re-enter password), always via ddp.
How can i do it?

Thanks in advance

Is there anybody who can help me?

If you are using accounts package;
Accounts._checkPassword(user, password);
on server method.

See for an example.