router enroll.go - "failed to parse JWT" could have various causes

[qrkourier]

failed to parse JWT

This error doesn't imply the full scope of failure modes that may cause enrollment to fail. It's because the triggering function validates that the token was signed by the pubkey of the server in the issuer claim (iss), which involves DNS resolution, creating a TCP stream with the controller, and completing TLS negotiation.

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Should we expand the error to imply more of the possible causes or find a way to surface the specific cause in a more focused error message?