Add email notifications for incomplete 2FA logins

An incomplete 2FA login is one where the correct master password was provided,
but the 2FA token or action required to complete the login was not provided
within the configured time limit. This potentially indicates that the user's
master password has been compromised, but the login was blocked by 2FA.

Be aware that the 2FA step can usually still be completed after the email
notification has already been sent out, which could be confusing. Therefore,
the incomplete 2FA time limit should be long enough that this situation would
be unlikely. This feature can also be disabled entirely if desired.

src/api/core/mod.rs

@@ -9,6 +9,7 @@ pub mod two_factor;
 pub use ciphers::purge_trashed_ciphers;
 pub use emergency_access::{emergency_notification_reminder_job, emergency_request_timeout_job};
 pub use sends::purge_sends;
+pub use two_factor::send_incomplete_2fa_notifications;
 
 pub fn routes() -> Vec<Route> {
     let mut mod_routes =

src/api/core/two_factor/mod.rs

@@ -1,3 +1,4 @@
+use chrono::{Duration, Utc};
 use data_encoding::BASE32;
 use rocket::Route;
 use rocket_contrib::json::Json;
@@ -7,7 +8,7 @@ use crate::{
     api::{JsonResult, JsonUpcase, NumberOrString, PasswordData},
     auth::Headers,
     crypto,
-    db::{models::*, DbConn},
+    db::{models::*, DbConn, DbPool},
     mail, CONFIG,
 };
 
@@ -156,3 +157,33 @@ fn disable_twofactor(data: JsonUpcase<DisableTwoFactorData>, headers: Headers, c
 fn disable_twofactor_put(data: JsonUpcase<DisableTwoFactorData>, headers: Headers, conn: DbConn) -> JsonResult {
     disable_twofactor(data, headers, conn)
 }
+
+pub fn send_incomplete_2fa_notifications(pool: DbPool) {
+    debug!("Sending notifications for incomplete 2FA logins");
+
+    if CONFIG.incomplete_2fa_time_limit() <= 0 || !CONFIG.mail_enabled() {
+        return;
+    }
+
+    let conn = match pool.get() {
+        Ok(conn) => conn,
+        _ => {
+            error!("Failed to get DB connection in send_incomplete_2fa_notifications()");
+            return;
+        }
+    };
+
+    let now = Utc::now().naive_utc();
+    let time_limit = Duration::minutes(CONFIG.incomplete_2fa_time_limit());
+    let incomplete_logins = TwoFactorIncomplete::find_logins_before(&(now - time_limit), &conn);
+    for login in incomplete_logins {
+        let user = User::find_by_uuid(&login.user_uuid, &conn).expect("User not found");
+        info!(
+            "User {} did not complete a 2FA login within the configured time limit. IP: {}",
+            user.email, login.ip_address
+        );
+        mail::send_incomplete_2fa_login(&user.email, &login.ip_address, &login.login_time, &login.device_name)
+            .expect("Error sending incomplete 2FA email");
+        login.delete(&conn).expect("Error deleting incomplete 2FA record");
+    }
+}