feat: implement CSRF protection across forms and routes

crates/presentation/src/csrf.rs

@@ -0,0 +1,58 @@
+use axum::{
+    extract::Request,
+    http::{HeaderValue, header},
+    middleware::Next,
+    response::Response,
+};
+
+#[derive(Clone)]
+pub struct CsrfToken(pub String);
+
+pub fn extract_from_cookie(headers: &axum::http::HeaderMap) -> Option<String> {
+    headers
+        .get(header::COOKIE)
+        .and_then(|v| v.to_str().ok())
+        .and_then(|cookies| {
+            cookies
+                .split(';')
+                .find_map(|c| c.trim().strip_prefix("csrf=").map(str::to_string))
+        })
+}
+
+fn secure_flag() -> &'static str {
+    if std::env::var("SECURE_COOKIES").as_deref() == Ok("true") {
+        "; Secure"
+    } else {
+        ""
+    }
+}
+
+pub async fn csrf_middleware(mut req: Request, next: Next) -> Response {
+    let existing = extract_from_cookie(req.headers());
+    let (token, needs_set) = match existing {
+        Some(t) => (t, false),
+        None => (uuid::Uuid::new_v4().to_string(), true),
+    };
+
+    req.extensions_mut().insert(CsrfToken(token.clone()));
+
+    let mut response = next.run(req).await;
+
+    if needs_set {
+        let cookie = format!(
+            "csrf={}; HttpOnly; Path=/; SameSite=Strict{}",
+            token,
+            secure_flag()
+        );
+        if let Ok(val) = HeaderValue::from_str(&cookie) {
+            response.headers_mut().append(header::SET_COOKIE, val);
+        }
+    }
+
+    response
+}
+
+/// Returns true if the form token does not match the cookie token.
+pub fn mismatch(token: &CsrfToken, form_value: &str) -> bool {
+    token.0 != form_value || form_value.is_empty()
+}