Properly return errors in Auth Interaction server

[mkurapov]

Context

Currently, in the auth server routes (Open Payments & some of the front channel routes), we are throwing GNAPServerRouteErrors, and properly catching them in gnapServerErrorMiddleware in order to return a well formatted GNAP error object that is defined in the GNAP spec. However, we are not doing the same for /grant/:id/:nonce/:choice /grant/:id/:nonce, the two routes exposed in the "Interaction Server".

Relevant OpenAPI docs

Todos

• Add gnapServerErrorMiddleware handler in the "Interaction Server" routes, add tests accordingly
• Update the IDP spec to display the different possible error objects for each route. A good idea might be to define all the possible GNAP errors we throw as components/schemas, and use them in each of the routes (see OpenAPI docs above)