Feature/authentication (#14)

* makes wsfs_server_config opaque

* feature: try to create mount point, if not present

* fixes server start failure due to existing mountpoint

* added basic authentication infrastructure

* makes wsfs_server_config opaque

* feature: try to create mount point, if not present

* fixes server start failure due to existing mountpoint

* added basic authentication infrastructure

* added unit tests for credentials

* added unit tests for authenticators

* propagates authenticators to server protocol

* enabled username authentication in daemon example

* adds example to compute password hash

* adds infrastructure to execute commands

* added userdb to encapsulate authentication stuff

* adds session and session_manager

* fixes warning about unused param

* moves some logic from server_protocol to session

* makes wsfs_server_config opaque

* feature: try to create mount point, if not present

* fixes server start failure due to existing mountpoint

* added basic authentication infrastructure

* makes wsfs_server_config opaque

* added unit tests for credentials

* added unit tests for authenticators

* propagates authenticators to server protocol

* enabled username authentication in daemon example

* adds example to compute password hash

* adds infrastructure to execute commands

* added userdb to encapsulate authentication stuff

* adds session and session_manager

* fixes warning about unused param

* moves some logic from server_protocol to session

* updates libcrypto to version 1.1.0

example/lib/userdb/include/userdb.h

@@ -0,0 +1,46 @@
+#ifndef USERDB_H
+#define USERDB_H
+
+#ifndef __cplusplus
+#include <stdbool.h>
+#endif
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+struct userdb;
+
+extern struct userdb * userdb_create(
+    char const * pepper);
+
+extern void userdb_dispose(struct userdb * db);
+
+extern bool userdb_save(
+    struct userdb * db,
+    char const * filename);
+
+extern bool userdb_load(
+    struct userdb * db,
+    char const * filename);
+
+extern void userdb_add(
+    struct userdb * db,
+    char const * username,
+    char const * password);
+
+extern void userdb_remove(
+    struct userdb * db,
+    char const * user);
+
+extern bool userdb_check(
+    struct userdb * db,
+    char const * username,
+    char const * password);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif