MXS-862: Implement GSSAPI backend authentication

The GSSAPI backend authentication is based on tokens.  The server first
sends the service principal name which is used for token generation. The
client then retrieves a token from the GSSAPI server which it sends to the
backend server. If the server can verify the authenticity of the token,
authentication is successful.

This module can be used with both GSSAPIAuth and MySQLAuth modules.

server/modules/authenticator/gssapi_auth_common.c

@@ -21,6 +21,8 @@ void* gssapi_auth_alloc()
     if (rval)
     {
         rval->state = GSSAPI_AUTH_INIT;
+        rval->principal_name = NULL;
+        rval->principal_name_len = 0;
     }
 
     return rval;
@@ -30,6 +32,40 @@ void gssapi_auth_free(void *data)
 {
     if (data)
     {
-        MXS_FREE(data);
+        gssapi_auth_t *auth = (gssapi_auth_t*)data;
+        MXS_FREE(auth->principal_name);
+        MXS_FREE(auth);
+    }
+}
+
+/**
+ * @brief Report GSSAPI errors
+ *
+ * @param major GSSAPI major error number
+ * @param minor GSSAPI minor error number
+ */
+void report_error(OM_uint32 major, OM_uint32 minor)
+{
+    OM_uint32 status_maj = major;
+    OM_uint32 status_min = minor;
+    OM_uint32 res = 0;
+    gss_buffer_desc buf = {0, 0};
+
+    major = gss_display_status(&minor, status_maj, GSS_C_GSS_CODE, NULL, &res, &buf);
+
+    {
+        char sbuf[buf.length + 1];
+        memcpy(sbuf, buf.value, buf.length);
+        sbuf[buf.length] = '\0';
+        MXS_ERROR("GSSAPI Major Error: %s", sbuf);
+    }
+
+    major = gss_display_status(&minor, status_min, GSS_C_MECH_CODE, NULL, &res, &buf);
+
+    {
+        char sbuf[buf.length + 1];
+        memcpy(sbuf, buf.value, buf.length);
+        sbuf[buf.length] = '\0';
+        MXS_ERROR("GSSAPI Minor Error: %s", sbuf);
     }
 }