Putting this here as a placeholder issue to be linked to for the inevitable flood of questions.
The certificate for minecraftforge.net is valid, however the intermediate certificate isn't being sent.
The Forge team are aware, the people who can fix it are currently away/sleeping.
A workaround is to add the intermediate certificate to your keystore, I won't be providing instructions as it involves security and I don't want to be liable.
Certificate problem has been fixed and ForgeGradle and such are working again.
You may need to restart any tools before they work.
cpw changed the cert we use to a single central one for all subdomains. And set it to send only our cert, thinking nginx's 'fullchain' config option would automatically combine necessary certs. Apparently it didn't.
Anyways this was just a temporary thing, that only effected some users {contrary to claims, as I tested on 4 different environments and didn't have issues in FG} but it's resolved now.
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cpw changed the cert we use to a single central one for all subdomains. And set it to send only our cert, thinking nginx's 'fullchain' config option would automatically combine necessary certs. Apparently it didn't.
Anyways this was just a temporary thing, that only effected some users {contrary to claims, as I tested on 4 different environments and didn't have issues in FG} but it's resolved now.