Add new "valid_flags" field to CERT_PKEY structure which determines what
the certificate can be used for (if anything). Set valid_flags field
in new tls1_check_chain function. Simplify ssl_set_cert_masks which used
to have similar checks in it.

Add new "cert_flags" field to CERT structure and include a "strict mode".
This enforces some TLS certificate requirements (such as only permitting
certificate signature algorithms contained in the supported algorithms
extension) which some implementations ignore: this option should be used
with caution as it could cause interoperability issues.

ssl/ssl.h

diff --git a/ssl/ssl.h b/ssl/ssl.h
index 2095d0f..3675d6e 100644
--- a/ssl/ssl.h
+++ b/ssl/ssl.h
@@ -650,6 +650,12 @@
  * or just freed (depending on the context's setting for freelist_max_len). */
 #define SSL_MODE_RELEASE_BUFFERS 0x00000010L
 
+/* Cert related flags */
+/* Many implementations ignore some aspects of the TLS standards such as
+ * enforcing certifcate chain algorithms. When this is set we enforce them.
+ */
+#define SSL_CERT_FLAG_TLS_STRICT	0x00000001L
+
 /* Note: SSL[_CTX]_set_{options,mode} use |= op on the previous value,
  * they cannot be used to clear bits. */
 
@@ -689,6 +695,15 @@
         SSL_ctrl((ssl),SSL_CTRL_TLS_EXT_SEND_HEARTBEAT,0,NULL)
 #endif
 
+#define SSL_CTX_set_cert_flags(ctx,op) \
+	SSL_CTX_ctrl((ctx),SSL_CTRL_CERT_FLAGS,(op),NULL)
+#define SSL_set_cert_flags(s,op) \
+	SSL_ctrl((s),SSL_CTRL_CERT_FLAGS,(op),NULL)
+#define SSL_CTX_clear_cert_flags(ctx,op) \
+	SSL_CTX_ctrl((ctx),SSL_CTRL_CLEAR_CERT_FLAGS,(op),NULL)
+#define SSL_clear_cert_flags(s,op) \
+	SSL_ctrl((s),SSL_CTRL_CLEAR_CERT_FLAGS,(op),NULL)
+
 void SSL_CTX_set_msg_callback(SSL_CTX *ctx, void (*cb)(int write_p, int version, int content_type, const void *buf, size_t len, SSL *ssl, void *arg));
 void SSL_set_msg_callback(SSL *ssl, void (*cb)(int write_p, int version, int content_type, const void *buf, size_t len, SSL *ssl, void *arg));
 #define SSL_CTX_set_msg_callback_arg(ctx, arg) SSL_CTX_ctrl((ctx), SSL_CTRL_SET_MSG_CALLBACK_ARG, 0, (arg))
@@ -1645,6 +1660,8 @@
 #define SSL_CTRL_SET_ECDH_AUTO			94
 #define SSL_CTRL_SET_SIGALGS			97
 #define SSL_CTRL_SET_SIGALGS_LIST		98
+#define SSL_CTRL_CERT_FLAGS			99
+#define SSL_CTRL_CLEAR_CERT_FLAGS		100
 
 #define DTLSv1_get_timeout(ssl, arg) \
 	SSL_ctrl(ssl,DTLS_CTRL_GET_TIMEOUT,0, (void *)arg)