MXS-862: Add authenticator options and instances

Authenticators now have a similar mechanism to the `router_options`
parameter which enables configurable authentication.

The authenticators also have a new initialize entry point which is similar
to the createInstance entry point of the filters and routers. The value of
`authenticator_options` is passed as a parameter to this function. The
return vaulue of the `initialize` entry point is passed to the `create`
entry point.

server/core/authenticator.c

@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl.
+ *
+ * Change Date: 2019-07-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <gw_authenticator.h>
+#include <modutil.h>
+#include <modules.h>
+#include <maxscale/alloc.h>
+
+/**
+ * @file authenticator.c - Authenticator module functions
+ */
+
+/**
+ * @brief Initialize an authenticator module
+ *
+ * Process the options into an array and pass them to the authenticator
+ * initialization function
+ *
+ * The authenticator must implement the @c initialize entry point if this
+ * function is called. If the authenticator does not implement this, behavior is
+ * undefined.
+ *
+ * @param func Authenticator entry point
+ * @param options Authenticator options
+ * @return Authenticator instance or NULL on error
+ */
+bool authenticator_init(void** dest, const char *authenticator, const char *options)
+{
+    bool rval = true;
+    void *instance = NULL;
+    GWAUTHENTICATOR *func = (GWAUTHENTICATOR*)load_module(authenticator, MODULE_AUTHENTICATOR);
+
+    if (func == NULL)
+    {
+        rval = false;
+    }
+    else if (func->initialize)
+    {
+        char *optarray[AUTHENTICATOR_MAX_OPTIONS + 1];
+        size_t optlen = options ? strlen(options) : 0;
+        char optcopy[optlen + 1];
+        int optcount = 0;
+
+        if (options)
+        {
+            strcpy(optcopy, options);
+            char *opt = optcopy;
+
+            while (opt && optcount < AUTHENTICATOR_MAX_OPTIONS)
+            {
+                char *end = strnchr_esc(opt, ',', sizeof(optcopy) - (opt - optcopy));
+
+                if (end)
+                {
+                    *end++ = '\0';
+                }
+
+                optarray[optcount++] = opt;
+                opt = end;
+            }
+        }
+
+        optarray[optcount] = NULL;
+
+        if ((instance = func->initialize(optarray)) == NULL)
+        {
+            rval = false;
+        }
+    }
+
+    *dest = instance;
+    return rval;
+}
+
+/**
+ * @brief Get the default authenticator for a protocol
+ *
+ * @param protocol Protocol to inspect
+ * @return The default authenticator for the protocol or NULL if the protocol
+ * does not provide one
+ */
+char* get_default_authenticator(const char *protocol)
+{
+    char *rval = NULL;
+    GWPROTOCOL *protofuncs = (GWPROTOCOL*)load_module(protocol, MODULE_PROTOCOL);
+
+    if (protofuncs && protofuncs->auth_default)
+    {
+        rval = MXS_STRDUP(protofuncs->auth_default());
+    }
+
+    return rval;
+}