diff mercurial/help/config.txt @ 28525:dfb21c34e07d

sslutil: allow multiple fingerprints per host

Certificate pinning via [hostfingerprints] is a useful security
feature. Currently, we only support one fingerprint per hostname.
This is simple but it fails in the real world:

* Switching certificates breaks clients until they change the
  pinned certificate fingerprint. This incurs client downtime
  and can require massive amounts of coordination to perform
  certificate changes.
* Some servers operate with multiple certificates on the same
  hostname.

This patch adds support for defining multiple certificate
fingerprints per host. This overcomes the deficiencies listed
above. I anticipate the primary use case of this feature will
be to define both the old and new certificate so a certificate
transition can occur with minimal interruption, so this scenario
has been called out in the help documentation.

--- a/mercurial/help/config.txt	Sun Mar 13 13:51:01 2016 -0700
+++ b/mercurial/help/config.txt	Sun Mar 13 14:03:58 2016 -0700
@@ -974,6 +974,9 @@
 This is very similar to how ssh known hosts works.
 
 The fingerprint is the SHA-1 hash value of the DER encoded certificate.
+Multiple values can be specified (separated by spaces or commas). This can
+be used to define both old and new fingerprints while a host transitions
+to a new certificate.
 
 The CA chain and web.cacerts is not used for servers with a fingerprint.