Thanos query and Thanos sidecar(on Prometheos pod) secure communication

Question

I have 5 GKE private clusters. On all clusters I have prom-stack chart deployed.(prometheus-community/kube-prometheus-stack version 52.0.1) On DevOps cluster I also have Thanos.(bitnami/thanos version 12.13.13) For Thanos query to be able to access all Thanos sidecars on the other clusters. I am using external LB.

  thanosServiceExternal:
    enabled: true
    loadBalancerIP: <IP>

That way my query is able to scrap them all.

My question is, how can I make the communication between the query and the sidecars more secure. Lets say with basic auth (I don't know about https, cause I think the query is using grpc protocol)

My query store conf:

query:
  dnsDiscovery:
    sidecarsService: prom-stack-devops-kube-pro-thanos-discovery
    sidecarsNamespace: monitoring
  stores:
    - "dns+<CLUSTER A IP>:10901"
    - "dns+<CLUSTER B IP>:10901"
    - "dns+<CLUSTER C IP>:10901"
    - "dns+<CLUSTER D IP>:10901"

I searched for basic auth conf for the query to use, and could'nt find any. Same goes for the sidecar. I can see basic auth conf for the Thanos itself (if lets say I want to Thanos as Grafana Data source)