Incorrect `iss` value on tokens, not the same as `issuer` value in OpenID configuration

When trying to log in to CSS using the run-against-css.sh script of the WAC tests, you get:

2021-08-11T12:45:33.820Z [DPoPWebIdExtractor] warn: Error verifying WebID via DPoP-bound access token: The access token issuer doesn't match its associated WebID's trusted OIDC issuers.
Actual: https://solidcommunity.net/
Expected: https://solidcommunity.net

So maybe we can change NSS to remove that trailing slash from the issuer?

Reproduce the mismatch with the WAC tests' run-against-css.sh entry point and inspect the DPoPWebIdExtractor path that verifies the token issuer against trusted OpenID issuers. Trace where NSS produces or reads the issuer value; done when the token and configuration values agree and the CSS login no longer reports an issuer mismatch.