parseAuthnResponse
Parses at.asitplus.openid.AuthenticationResponseParameters, where input is either:
a URL, containing parameters in the fragment, e.g.
https://example.com#id_token=...a URL, containing parameters in the query, e.g.
https://example.com?id_token=...parameters encoded as a POST body, e.g.
id_token=...&vp_token=...