feat: Start dummy in-memory database

src/db/common.rs

@@ -0,0 +1,36 @@
+use tokio::sync::RwLock;
+
+use std::sync::Arc;
+
+use crate::db::{DatabaseInterface, UserRef};
+
+#[derive(Clone, Debug)]
+pub struct Database<D: DatabaseInterface> {
+    pub inner: Arc<RwLock<D>>,
+}
+
+impl<D: DatabaseInterface> Database<D> {
+    pub fn new(db: D) -> Self {
+        Self {
+            inner: Arc::new(RwLock::new(db)),
+        }
+    }
+}
+
+impl<D: DatabaseInterface> Database<D> {
+    /// Return false if the user doesn't exist, or the password is wrong.
+    ///
+    /// TODO: should we return something else when the account doesn't exist?
+    ///       or is it a feature to behave in the same way?
+    ///
+    /// TODO: we may want to make sure the method runs in constant time
+    ///       to avoid leaking information about existing users...
+    ///       or maybe we do not care.
+    async fn check_password(&self, user: &UserRef, password: &str) -> bool {
+        let Some(user) = self.get_user(user).await else {
+            return false;
+        };
+
+        user.password == password
+    }
+}