Route-Emitter: Support mTLS-only authentication with NATS

[domdom82]

Enter an issue title

Add support for mTLS-only authentication with NATS for Route-Emitter

Summary

With the adoption of nats-tls we now have client authentication built-in with the mTLS handshake that verifies the client certificate.
This makes the additional basic authentication with the "nats" user obsolete. Currently, the erb for route-emitter requires a username and password to be set via the bosh link. This PR makes the template rendering of route-emitter work even when there is no user and password set by NATS.

Diego repo

route-emitter

Describe alternatives you've considered (optional)

An alternative to outright removing the password on NATS side would have been to set a default of "" (empty string) for the NATS password which would have made sure that there is a password and user set at all times. This would have made this PR unnecessary because the link property would always be set. However, I refrained from this approach because empty passwords are bad practise. So on cf-deployment level there should either be set a meaningful (secure) password or no password at all - which is now possible.

Additional Text Output, Screenshots, or contextual information (optional)

There is a slack conversation about the issue.

Since this basically affects all NATS clients and the NATS release, there are a set of PRs to be merged as companions to this PR:

NATS-release: cloudfoundry/nats-release#39
routing-release: cloudfoundry/routing-release#244
metrics-discovery-release: cloudfoundry/metrics-discovery-release#14

Once they are all merged, you can remove this section from cf-deployment.yml. This could be done directly or via an ops-file that keeps the basic authentication as a default.

[ameowlia]

Oops, I somehow missed this issue in my mass-merge event. It looks like this can be closed now.

❓ @domdom82 - can you close this issue or point out what is left to do here?

Thanks!

[xavierW]

 邮件已收到，我会尽快阅读并回复，谢谢

[domdom82]

@ameowlia I opened it as an enhancement to follow the guidelines for diego PRs. Closing as it is merged now.