Description
Add x-fowarded-client-cert information on trusted incoming connections.
Envoy provides support forwarding and annotating the
x-forwarded-client-cert header via the forward_client_cert_details
set_current_client_cert_details filter fields. It would be helpful for
consul to support this directly in its config. The escape hatches are
a bit cumbersome for this purpose.
This has been implemented on incoming connections to envoy. Outgoing
(from the local service through the sidecar) will not have a
certificate, and so are left alone.
A service on an incoming connection will now get headers something like this:
```
X-Forwarded-Client-Cert:[By=spiffe://efad7282-d9b2-3298-f6d8-38b37fb58df3.consul/ns/default/dc/dc1/svc/counting;Hash=61ad5cbdfcb50f5a3ec0ca60923d61613c149a9d4495010a64175c05a0268ab2;Cert="-----BEGIN%20CERTIFICATE-----%0AMIICHDCCAcOgAwIBAgIBCDAKBggqhkjOPQQDAjAxMS8wLQYDVQQDEyZwcmktMTli%0AYXdyb2YuY29uc3VsLmNhLmVmYWQ3MjgyLmNvbnN1bDAeFw0yMjA0MjkwMzE0NTBa%0AFw0yMjA1MDIwMzE0NTBaMAAwWTATBgcqhkjOPQIBBggqhkjOPQMBBwNCAARVIZ7Y%0AZEXfbOGBfxGa7Vuok1MIng%2FuzLQK2xLVlSTIPDbO5hstTGP%2B%2FGx182PYFP3jYqk5%0Aq6rYWe1wiPNMA30Io4H8MIH5MA4GA1UdDwEB%2FwQEAwIDuDAdBgNVHSUEFjAUBggr%0ABgEFBQcDAgYIKwYBBQUHAwEwDAYDVR0TAQH%2FBAIwADApBgNVHQ4EIgQgrp4q50oX%0AHHghMbxz5Bk8OJFWMdfgH0Upr350WlhyxvkwKwYDVR0jBCQwIoAgUe6uERAIj%2FLM%0AyuFzDc3Wbp9TGAKBJYAwyhF14ToOQCMwYgYDVR0RAQH%2FBFgwVoZUc3BpZmZlOi8v%0AZWZhZDcyODItZDliMi0zMjk4LWY2ZDgtMzhiMzdmYjU4ZGYzLmNvbnN1bC9ucy9k%0AZWZhdWx0L2RjL2RjMS9zdmMvZGFzaGJvYXJkMAoGCCqGSM49BAMCA0cAMEQCIDwb%0AFlchufggNTijnQ5SUcvTZrWlZyq%2FrdVC20nbbmWLAiAVshNNv1xBqJI1NmY2HI9n%0AgRMfb8aEPVSuxEHhqy57eQ%3D%3D%0A-----END%20CERTIFICATE-----%0A";Chain="-----BEGIN%20CERTIFICATE-----%0AMIICHDCCAcOgAwIBAgIBCDAKBggqhkjOPQQDAjAxMS8wLQYDVQQDEyZwcmktMTli%0AYXdyb2YuY29uc3VsLmNhLmVmYWQ3MjgyLmNvbnN1bDAeFw0yMjA0MjkwMzE0NTBa%0AFw0yMjA1MDIwMzE0NTBaMAAwWTATBgcqhkjOPQIBBggqhkjOPQMBBwNCAARVIZ7Y%0AZEXfbOGBfxGa7Vuok1MIng%2FuzLQK2xLVlSTIPDbO5hstTGP%2B%2FGx182PYFP3jYqk5%0Aq6rYWe1wiPNMA30Io4H8MIH5MA4GA1UdDwEB%2FwQEAwIDuDAdBgNVHSUEFjAUBggr%0ABgEFBQcDAgYIKwYBBQUHAwEwDAYDVR0TAQH%2FBAIwADApBgNVHQ4EIgQgrp4q50oX%0AHHghMbxz5Bk8OJFWMdfgH0Upr350WlhyxvkwKwYDVR0jBCQwIoAgUe6uERAIj%2FLM%0AyuFzDc3Wbp9TGAKBJYAwyhF14ToOQCMwYgYDVR0RAQH%2FBFgwVoZUc3BpZmZlOi8v%0AZWZhZDcyODItZDliMi0zMjk4LWY2ZDgtMzhiMzdmYjU4ZGYzLmNvbnN1bC9ucy9k%0AZWZhdWx0L2RjL2RjMS9zdmMvZGFzaGJvYXJkMAoGCCqGSM49BAMCA0cAMEQCIDwb%0AFlchufggNTijnQ5SUcvTZrWlZyq%2FrdVC20nbbmWLAiAVshNNv1xBqJI1NmY2HI9n%0AgRMfb8aEPVSuxEHhqy57eQ%3D%3D%0A-----END%20CERTIFICATE-----%0A";Subject="";URI=spiffe://efad7282-d9b2-3298-f6d8-38b37fb58df3.consul/ns/default/dc/dc1/svc/dashboard]
```
Closes#12852
