istio.io/content/docs/ops/security/mutual-tls/index.md

title	description	weight
Mutual TLS	What to do if mutual TLS authentication isn't working.	30

If you suspect problems with mutual TLS, first ensure that Citadel is healthy, and second ensure that keys and certificates are being delivered to sidecars properly.

If everything appears to be working so far, the next step is to verify that the right authentication policy is applied and the right destination rules are in place.