Making JWT token audience/issuer validation case insensitive.

[mathewc]

Backport of #9678. In the v1 port, I didn't carry the logging forward because the version of the token libraries we're using in v1 make it easy to log PII when logging token validation exceptions (e.g. will log the raw token). Later library versions being used in v3/v4 do not output PII.

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