SIOP is currently limited to interactions on the device where the SIOP OP is located. However, there are use cases where the user might want to use the keys and credentials in her SIOP to login/identify on a different device. Example are mDL, kiosks or a website visited on the user’s desktop PC.
There is a adopted SIOP flow being proposed in the mDL context, where the first request from RP to SIOP is conveyed using request object/URL and the SIOP sends a POST request to the RP‘s backend. I suggest to add this flow (or a similar flow) to SIOP v2 in order to support the beforementioned use cases.