Add JWKS endpoint to HTTP API for exposing the root public signing keys used for signing workload identity JWTs.
Part 1 of N components as part of making workload identities consumable by third party services such as Consul and Vault. Identity attenuation (audience) and expiration (+renewal) are necessary to securely use workload identities with 3rd parties, so this merge does not yet document this endpoint.
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Co-authored-by: Tim Gross <tgross@hashicorp.com>
