Getting signed data from the server

[mpalmer (Matt Palmer)]

@EGreg

We should be able to use Discourse to authenticate the user.

Yes, you should, and you can. This is what the Discourse SSO protocol is for. That linked topic is written from the perspective of Discourse authenticating to an external auth provider, but Discourse can also act as the auth provider to a different app (an example of which is the discourse-auth-proxy, using the same protocol.