SecureSocket: add some certificate support

* Instead of creating an OpenSSL context ofor each socket, use a global
one and initialize it lazily when the first SecureSocket is created
* Load the certificates from our certificate list so SSL certificates
sent by servers can be validated.
* Add a callback for signalling that certificate validation failed, the
default implementation proceeds with the connection anyway (to keep the
old behavior).
* Introduce BCertificate class, that provides some information about a
certificate. Currently it's only used by the callback mentionned above,
but it will be possible to get the leaf certificate for the connection
after it's established.

Review of the API and implementation is welcome, before I start making
use of this in HttpRequest and WebKit to allow the user to accept new
certificates.

headers/os/net/Certificate.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2014 Haiku, Inc.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _CERTIFICATE_H
+#define _CERTIFICATE_H
+
+
+#include <SecureSocket.h>
+#include <String.h>
+
+
+class BCertificate {
+public:
+				~BCertificate();
+
+	BString		String();
+
+	bigtime_t	StartDate();
+	bigtime_t	ExpirationDate();
+	BString		Issuer();
+	BString		Subject();
+
+private:
+	friend class BSecureSocket::Private;
+	class Private;
+				BCertificate(Private* data);
+
+	Private*	fPrivate;
+};
+
+#endif

headers/os/net/SecureSocket.h

@@ -9,6 +9,9 @@
 #include <Socket.h>
 
 
+class BCertificate;
+
+
 class BSecureSocket : public BSocket {
 public:
 								BSecureSocket();
@@ -17,6 +20,10 @@ public:
 								BSecureSocket(const BSecureSocket& other);
 	virtual						~BSecureSocket();
 
+	virtual bool				CertificateVerificationFailed(BCertificate);
+
+	// BSocket implementation
+
 	virtual	status_t			Connect(const BNetworkAddress& peer,
 									bigtime_t timeout = B_INFINITE_TIMEOUT);
 	virtual	void				Disconnect();
@@ -30,6 +37,7 @@ public:
 	virtual ssize_t				Write(const void* buffer, size_t size);
 
 private:
+	friend class BCertificate;
 			class Private;
 			Private*			fPrivate;
 };