diff --git a/codecov.yml b/codecov.yml
index e00ce3d..ed17c6f 100644
--- a/codecov.yml
+++ b/codecov.yml
@@ -1,2 +1,7 @@
+coverage:
+  status:
+    project:
+      default:
+        threshold: 0.5%
 github_checks:
   annotations: false
diff --git a/cot/src/auth.rs b/cot/src/auth.rs
index 026287d..d342cd6 100644
--- a/cot/src/auth.rs
+++ b/cot/src/auth.rs
@@ -40,6 +40,14 @@ pub enum AuthError {
     /// An error occurred while accessing the user object.
     #[error("Error while accessing the user object")]
     UserBackend(#[source] Box<dyn std::error::Error + Send + Sync + 'static>),
+    /// The credentials type provided to [`AuthBackend::authenticate`] is not
+    /// supported.
+    #[error("Tried to authenticate with an unsupported credentials type")]
+    CredentialsTypeNotSupported,
+    /// The [`UserId`] type provided to [`AuthBackend::get_user_by_id`] is not
+    /// supported.
+    #[error("Tried to get a user by an unsupported user ID type")]
+    UserIdTypeNotSupported,
 }
 
 impl AuthError {
@@ -958,6 +966,8 @@ pub trait AuthBackend: Send + Sync {
     /// # Errors
     ///
     /// Returns an error if the user object cannot be fetched.
+    ///
+    /// Returns an error if the credentials type is not supported.
     async fn authenticate(
         &self,
         request: &Request,
@@ -973,6 +983,8 @@ pub trait AuthBackend: Send + Sync {
     ///
     /// Returns an error if the user object cannot be fetched.
     ///
+    /// Returns an error if the user ID type is not supported.
+    ///
     /// # Examples
     ///
     /// ```
diff --git a/cot/src/auth/db.rs b/cot/src/auth/db.rs
index 1320204..5457eb6 100644
--- a/cot/src/auth/db.rs
+++ b/cot/src/auth/db.rs
@@ -146,7 +146,7 @@ impl DatabaseUser {
     ///     )
     ///     .await?;
     ///
-    ///     let user_from_db = DatabaseUser::get_by_id(request.db(), UserId::Int(user.id())).await?;
+    ///     let user_from_db = DatabaseUser::get_by_id(request.db(), user.id()).await?;
     ///
     ///     Ok(Response::new_html(
     ///         StatusCode::OK,
@@ -167,9 +167,7 @@ impl DatabaseUser {
     /// #     Ok(())
     /// # }
     /// ```
-    pub async fn get_by_id<DB: DatabaseBackend>(db: &DB, id: UserId) -> Result<Option<Self>> {
-        let id = id.as_int().expect("User ID should be an integer");
-
+    pub async fn get_by_id<DB: DatabaseBackend>(db: &DB, id: i64) -> Result<Option<Self>> {
         let db_user = query!(DatabaseUser, $id == id)
             .get(db)
             .await
@@ -503,7 +501,7 @@ impl AuthBackend for DatabaseUserBackend {
                 .await
                 .map(|user| user.map(|user| Box::new(user) as Box<dyn User + Send + Sync>))?)
         } else {
-            Ok(None)
+            Err(AuthError::CredentialsTypeNotSupported)
         }
     }
 
@@ -512,6 +510,10 @@ impl AuthBackend for DatabaseUserBackend {
         request: &Request,
         id: UserId,
     ) -> Result<Option<Box<dyn User + Send + Sync>>> {
+        let UserId::Int(id) = id else {
+            return Err(AuthError::UserIdTypeNotSupported);
+        };
+
         #[allow(trivial_casts)] // Upcast to the correct Box type
         Ok(DatabaseUser::get_by_id(request.db(), id)
             .await?
@@ -648,9 +650,7 @@ mod tests {
             .expect_get::<DatabaseUser>()
             .returning(move |_| Ok(Some(user.clone())));
 
-        let result = DatabaseUser::get_by_id(&mock_db, UserId::Int(1))
-            .await
-            .unwrap();
+        let result = DatabaseUser::get_by_id(&mock_db, 1).await.unwrap();
         assert!(result.is_some());
         assert_eq!(result.unwrap().username(), "testuser");
     }