Fix implementation of VERIFY_OPTIONAL verification mode
This commit changes the behaviour of mbedtls_ssl_parse_certificate
to make the two authentication modes SSL_VERIFY_REQUIRED and
SSL_VERIFY_OPTIONAL be in the following relationship:
Mode == SSL_VERIFY_REQUIRED
<=> Mode == SSL_VERIFY_OPTIONAL + check verify result
Also, it changes the behaviour to perform the certificate chain
verification even if the trusted CA chain is empty. Previously, the
function failed in this case, even when using optional verification,
which was brought up in #864.
diff --git a/library/x509_crt.c b/library/x509_crt.c
index a3517f6..16a29b5 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -1403,6 +1403,7 @@
{ BADCERT_KEY_USAGE, "Usage does not match the keyUsage extension" },
{ BADCERT_EXT_KEY_USAGE, "Usage does not match the extendedKeyUsage extension" },
{ BADCERT_NS_CERT_TYPE, "Usage does not match the nsCertType extension" },
+ { BADCERT_BAD_KEY, "The certificate uses an invalid key (e.g. unsupported elliptic curve)" },
{ 0, NULL }
};