make auth.salt parameter optional

Used implementation of the hasher includes salt itself, thus additional
salt is optional and can be safely (in terms of security) treat as empty
string

src/ahriman/application/handlers/users.py

@@ -52,7 +52,7 @@ class Users(Handler):
         if args.action == Action.Update:
             user = Users.user_create(args)
             # if password is left blank we are not going to require salt to be set
-            salt = configuration.get("auth", "salt") if user.password else ""
+            salt = configuration.get("auth", "salt", fallback="") if user.password else ""
             database.user_update(user.hash_password(salt))
         elif args.action == Action.List:
             users = database.user_list(args.username, args.role)

src/ahriman/core/auth/mapping.py

@@ -46,7 +46,7 @@ class Mapping(Auth):
         """
         Auth.__init__(self, configuration, provider)
         self.database = database
-        self.salt = configuration.get("auth", "salt")
+        self.salt = configuration.get("auth", "salt", fallback="")
 
     async def check_credentials(self, username: str | None, password: str | None) -> bool:
         """

src/ahriman/core/configuration/schema.py

@@ -93,9 +93,12 @@ CONFIGURATION_SCHEMA: ConfigurationSchema = {
                 "type": "string",
                 "oneof": [
                     {"allowed": ["disabled"]},
-                    {"allowed": ["configuration", "mapping"], "dependencies": ["salt"]},
+                    {"allowed": ["configuration", "mapping"]},
                     {"allowed": ["oauth"], "dependencies": [
-                        "client_id", "client_secret", "oauth_provider", "oauth_scopes", "salt"
+                        "client_id",
+                        "client_secret",
+                        "oauth_provider",
+                        "oauth_scopes",
                     ]},
                 ],
             },