LTI 1.3 : What to do with the id_token in Step 4

Community Champion

I've setting up a hello world LTI 1.3 ,and I've got it working to the point that I'm getting back what appears to be a valid 


I can take this id_token, and paste it into and I can see expected results.

What I can't figure out is what is doing to decode/decrypt this id-token.   The docs say

But the linked docs don't say "How" to perform this verification.    

What is the workflow for decoding and validating the id_token once we've gotten it?