Add SCRAM-SHA-1 support

This adds the new base class XMPPAuthenticator and the derived
classes XMPPSCRAMAuth and XMPPPLAINAuth.
They are now used for authentication from within XMPPConnection.

Also adds XMPPAuthFailedException which is thrown in appropriate places.

src/XMPPAuthenticator.h

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2011, Florian Zeitz <florob@babelmonkeys.de>
+ *
+ * https://webkeks.org/hg/objxmpp/
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice is present in all copies.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#import <ObjFW/ObjFW.h>
+
+/**
+ * \brief A base class for classes implementing authentication mechanisms
+ */
+@interface XMPPAuthenticator: OFObject
+{
+	/// The authzid to get authorization for
+	OFString *authzid;
+	/// The authcid to authenticate with
+	OFString *authcid;
+	/// The password to authenticate with
+	OFString *password;
+}
+@property (copy) OFString *authzid;
+@property (copy) OFString *authcid;
+@property (copy) OFString *password;
+
+/**
+ * Initializes an already allocated XMPPAuthenticator with an authcid
+ * and password.
+ *
+ * \param authcid The authcid to authenticate with
+ * \param password The password to authenticate with
+ * \return A initialized XMPPAuthenticator
+ */
+- initWithAuthcid: (OFString*)authcid
+	 password: (OFString*)password;
+
+/**
+ * Initializes an already allocated XMPPSCRAMAuthenticator with an authzid,
+ * authcid and password.
+ *
+ * \param authzid The authzid to get authorization for
+ * \param authcid The authcid to authenticate with
+ * \param password The password to authenticate with
+ * \return A initialized XMPPAuthenticator
+ */
+- initWithAuthzid: (OFString*)authzid
+	  authcid: (OFString*)authcid
+	 password: (OFString*)password;
+
+/**
+ * \return A OFDataAray containing the initial authentication message
+ */
+- (OFDataArray*)getClientFirstMessage;
+
+/**
+ * \param challenge The challenge to generate a response for
+ * \return The response to the given challenge
+ */
+- (OFDataArray*)getResponseWithChallenge: (OFDataArray*)challenge;
+
+/**
+ * Checks whether the servers final message was valid
+ *
+ * \param  message The servers final message
+ */
+- (void)parseServerFinalMessage: (OFDataArray*)message;
+@end