For people having issues with CA - It is not the CA that is the problem (it is not a famous CA, but is known, at least by Chrome), the problem is that they probably shortened the domain too late and are still using the old configuration. Use the URL below, the certificate works fine. It's just for the wrong domain:
Edit: I'm unable to login though. I get the OTP from Aadhaar just fine, but the website doesn't seem to be able to verify it.
Edit 2: It worked after a couple of tries. Looking at the trail, it is probably some issue with Aadhaar and not this website. It does look really neat. You basically upload copies of your IDs and then agencies can request it. You get to approve. They are pulling UID data so it's quick to set up. I think the point of this is that you can link all other IDs with UID so people just have to ask for you Aadhaar number, no paper ID copies or forms. I wish they just integrated this into UID system like they link bank accounts, that way developers would have a single UIDAI API for identity, bank accounts and other IDs.