feat(auth): add username sign-in mode and recovery kits (#3215)

fluxer_admin/src/utils/forms.rs

@@ -55,6 +55,10 @@ impl MultiValueForm {
         self.fields.contains_key(key)
     }
 
+    pub fn has_key_starting_with(&self, prefix: &str) -> bool {
+        self.fields.keys().any(|key| key.starts_with(prefix))
+    }
+
     pub fn values(&self, key: &str) -> &[String] {
         self.fields.get(key).map(Vec::as_slice).unwrap_or_default()
     }

fluxer_admin/src/utils/mod.rs

@@ -3,3 +3,4 @@
 pub mod bigint;
 pub mod forms;
 pub mod timestamps;
+pub mod user_tag;

fluxer_admin/src/utils/user_tag.rs

@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+use std::future::Future;
+
+tokio::task_local! {
+    static UNIQUE_USERNAMES: bool;
+}
+
+pub async fn with_unique_usernames<F: Future>(unique_usernames: bool, future: F) -> F::Output {
+    UNIQUE_USERNAMES.scope(unique_usernames, future).await
+}
+
+pub fn sync_with_unique_usernames<R>(unique_usernames: bool, f: impl FnOnce() -> R) -> R {
+    UNIQUE_USERNAMES.sync_scope(unique_usernames, f)
+}
+
+pub fn unique_usernames() -> bool {
+    UNIQUE_USERNAMES.try_with(|value| *value).unwrap_or(false)
+}
+
+pub fn shows_discriminator(discriminator: &str, is_bot: bool) -> bool {
+    is_bot || !unique_usernames() || discriminator.trim().parse::<u16>() != Ok(0)
+}
+
+pub fn user_tag(username: &str, discriminator: &str, is_bot: bool) -> String {
+    if shows_discriminator(discriminator, is_bot) {
+        format!("{username}#{discriminator}")
+    } else {
+        username.to_owned()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn email_mode_keeps_every_tag() {
+        assert_eq!(user_tag("alice", "0000", false), "alice#0000");
+        assert_eq!(user_tag("alice", "0042", false), "alice#0042");
+        sync_with_unique_usernames(false, || {
+            assert_eq!(user_tag("alice", "0000", false), "alice#0000");
+            assert_eq!(user_tag("bot", "0000", true), "bot#0000");
+        });
+    }
+
+    #[test]
+    fn username_mode_hides_zero_tag_for_humans() {
+        sync_with_unique_usernames(true, || {
+            assert_eq!(user_tag("alice", "0000", false), "alice");
+            assert_eq!(user_tag("alice", "0", false), "alice");
+            assert!(!shows_discriminator("0000", false));
+        });
+    }
+
+    #[test]
+    fn username_mode_keeps_bot_and_non_zero_tags() {
+        sync_with_unique_usernames(true, || {
+            assert_eq!(user_tag("helper", "4363", true), "helper#4363");
+            assert_eq!(user_tag("helper", "0000", true), "helper#0000");
+            assert_eq!(user_tag("legacy", "0042", false), "legacy#0042");
+        });
+    }
+
+    #[test]
+    fn mode_defaults_to_email_outside_a_request() {
+        assert!(!unique_usernames());
+    }
+}