tls-checktrust

tls-checktrust is a variable defined in `tls.el'.
Its value is

nil

Documentation:
Indicate if certificates should be checked against trusted root certs.
If this is `ask', the user can decide whether to accept an
untrusted certificate. You may have to adapt `tls-program' in
order to make this feature work properly, i.e., to ensure that
the external program knows about the root certificates you
consider trustworthy, e.g.:

(setq tls-program
'("gnutls-cli --x509cafile /etc/ssl/certs/ca-certificates.crt -p %p %h"
"gnutls-cli --x509cafile /etc/ssl/certs/ca-certificates.crt -p %p %h --protocols ssl3"
"openssl s_client -connect %h:%p -CAfile /etc/ssl/certs/ca-certificates.crt -no_ssl2 -ign_eof"))

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.1 of Emacs.