This conversation reminds me of another one - discourse is doing so much better at all of this and is getting better all the time, while other platforms (like wordpress) are not keeping with the times. So it may be worthwhile to make it easier to use discourse as the SSO source… as part of the wp-discourse wordpress plugin, for example.
https://meta.discourse.org/t/discourse-as-sso-source-of-authority-for-wordpress/18400
But this idea of @plkap74 is also very interesting - why not just still keep that layer of validation in discourse so when the user comes over from the other site they can be verified again. Perhaps we could then also still benefit from other discourse features that we lose with SSO, like the invites system, which I sorely miss!