doc: specify ca cert needs to be shared

[schmichael]

(Certificate management is the worst.)

Had some confusion from a user thinking they had to use a lb/proxy to configure the Vault integration. I noticed our docs about mTLS/verify_client lacked mentioning that Vault needs to trust Nomad's CA, so I added some words to hopefully make that more clear? The words do not seem like good words so if you have gooder words please suggest them.

[david-yu]

I'm curious does that mean creating the Vault auth method for nomad with that public CA via the certificate parameter? https://developer.hashicorp.com/vault/docs/auth/cert#configuration

[schmichael]

I'm curious does that mean creating the Vault auth method for nomad with that public CA via the certificate parameter? https://developer.hashicorp.com/vault/docs/auth/cert#configuration

Hm, that certificate parameter is for the certificate auth method, not the JWT auth method. Poking around I think jwks_ca_pem is the parameter people can configure the certificate with?

I'll update the docs to point people to it directly.

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