Test for trialing slashes in value for 'issuer' from '/.well-known/openid-configuration' responses

Basically our ESS Brokers are advertising themselves (in their /.well-known/openid-configuration responses) as issuers with a trailing slash, e.g. for https://broker.pod.inrupt.com/.well-known/openid-configuration:

{
    "introspection_endpoint": "https://broker.pod.inrupt.com/introspect",
    "scopes_supported": [
        "openid",
        "offline_access",
        "webid"
    ],
    "issuer": "https://broker.pod.inrupt.com/",
    :

Note the trailing slash on the issuer URL (which is technically (slightly!) more correct than having the URL without the trailing slash).
So it seems NSS might be blindly taking that issuer value, and appending the string literal /.well-known/openid-configuration to it, without first checking if the issuer value has a trailing slash or not. If the URL constructed has two slashes, then the server responds with it’s standard HTML ‘Page Not Found’ response, which results in the ‘invalid json response…’ error.

If this is correct, then the fix in NSS should be simply checking for a trailing slash before appending /.well-known/openid-configuration.

Inizia individuando il codice che costruisce l'URL /.well-known/openid-configuration a partire dall'issuer restituito dalla risposta di configurazione OpenID. Aggiungi la copertura per i valori di issuer con e senza una barra finale e verifica che entrambi producano un URL valido con una sola barra, anziché una risposta JSON non valida.