diff --git a/model/src/lib.rs b/model/src/lib.rs
index 168ae88..9ca9d52 100644
--- a/model/src/lib.rs
+++ b/model/src/lib.rs
@@ -68,6 +68,12 @@ pub struct CreateGroupRequest {
     pub display_name: String,
 }
 
+#[derive(PartialEq, Eq, Debug, Serialize, Deserialize)]
+pub struct AddUserToGroupRequest {
+    pub user_id: String,
+    pub group_id: i32,
+}
+
 #[derive(Clone, Serialize, Deserialize)]
 pub struct JWTClaims {
     pub exp: DateTime<Utc>,
diff --git a/src/domain/handler.rs b/src/domain/handler.rs
index 2eb33ce..b348b56 100644
--- a/src/domain/handler.rs
+++ b/src/domain/handler.rs
@@ -11,6 +11,7 @@ pub trait BackendHandler: Clone + Send {
     async fn list_groups(&self) -> Result<Vec<Group>>;
     async fn create_user(&self, request: CreateUserRequest) -> Result<()>;
     async fn create_group(&self, request: CreateGroupRequest) -> Result<i32>;
+    async fn add_user_to_group(&self, request: AddUserToGroupRequest) -> Result<()>;
     async fn get_user_groups(&self, user: String) -> Result<HashSet<String>>;
 }
 
@@ -28,5 +29,6 @@ mockall::mock! {
         async fn create_user(&self, request: CreateUserRequest) -> Result<()>;
         async fn create_group(&self, request: CreateGroupRequest) -> Result<i32>;
         async fn get_user_groups(&self, user: String) -> Result<HashSet<String>>;
+        async fn add_user_to_group(&self, request: AddUserToGroupRequest) -> Result<()>;
     }
 }
diff --git a/src/domain/sql_backend_handler.rs b/src/domain/sql_backend_handler.rs
index 643814f..d6ed2bf 100644
--- a/src/domain/sql_backend_handler.rs
+++ b/src/domain/sql_backend_handler.rs
@@ -242,6 +242,7 @@ impl BackendHandler for SqlBackendHandler {
         sqlx::query(&query).execute(&self.sql_pool).await?;
         Ok(())
     }
+
     async fn create_group(&self, request: CreateGroupRequest) -> Result<i32> {
         let query = Query::insert()
             .into_table(Groups::Table)
@@ -255,8 +256,17 @@ impl BackendHandler for SqlBackendHandler {
             .and_where(Expr::col(Groups::DisplayName).eq(request.display_name.as_str()))
             .to_string(DbQueryBuilder {});
         let row = sqlx::query(&query).fetch_one(&self.sql_pool).await?;
-        Ok(
-            row.get::<i32, _>(&*Groups::GroupId.to_string()))
+        Ok(row.get::<i32, _>(&*Groups::GroupId.to_string()))
+    }
+
+    async fn add_user_to_group(&self, request: AddUserToGroupRequest) -> Result<()> {
+        let query = Query::insert()
+            .into_table(Memberships::Table)
+            .columns(vec![Memberships::UserId, Memberships::GroupId])
+            .values_panic(vec![request.user_id.into(), request.group_id.into()])
+            .to_string(DbQueryBuilder {});
+        sqlx::query(&query).execute(&self.sql_pool).await?;
+        Ok(())
     }
 }
 
@@ -288,16 +298,22 @@ mod tests {
     }
 
     async fn insert_group(handler: &SqlBackendHandler, name: &str) -> i32 {
-        handler.create_group(CreateGroupRequest{display_name: name.to_string()}).await.unwrap()
+        handler
+            .create_group(CreateGroupRequest {
+                display_name: name.to_string(),
+            })
+            .await
+            .unwrap()
     }
 
-    async fn insert_membership(sql_pool: &Pool, group_id: i32, user_id: &str) {
-        let query = Query::insert()
-            .into_table(Memberships::Table)
-            .columns(vec![Memberships::UserId, Memberships::GroupId])
-            .values_panic(vec![user_id.into(), group_id.into()])
-            .to_string(DbQueryBuilder {});
-        sqlx::query(&query).execute(sql_pool).await.unwrap();
+    async fn insert_membership(handler: &SqlBackendHandler, group_id: i32, user_id: &str) {
+        handler
+            .add_user_to_group(AddUserToGroupRequest {
+                user_id: user_id.to_string(),
+                group_id,
+            })
+            .await
+            .unwrap();
     }
 
     #[tokio::test]
@@ -437,10 +453,10 @@ mod tests {
         insert_user(&handler, "John", "Pa33w0rd!").await;
         let group_1 = insert_group(&handler, "Best Group").await;
         let group_2 = insert_group(&handler, "Worst Group").await;
-        insert_membership(&sql_pool, group_1, "bob").await;
-        insert_membership(&sql_pool, group_1, "patrick").await;
-        insert_membership(&sql_pool, group_2, "patrick").await;
-        insert_membership(&sql_pool, group_2, "John").await;
+        insert_membership(&handler, group_1, "bob").await;
+        insert_membership(&handler, group_1, "patrick").await;
+        insert_membership(&handler, group_2, "patrick").await;
+        insert_membership(&handler, group_2, "John").await;
         assert_eq!(
             handler.list_groups().await.unwrap(),
             vec![
@@ -466,9 +482,9 @@ mod tests {
         insert_user(&handler, "John", "Pa33w0rd!").await;
         let group_1 = insert_group(&handler, "Group1").await;
         let group_2 = insert_group(&handler, "Group2").await;
-        insert_membership(&sql_pool, group_1, "bob").await;
-        insert_membership(&sql_pool, group_1, "patrick").await;
-        insert_membership(&sql_pool, group_2, "patrick").await;
+        insert_membership(&handler, group_1, "bob").await;
+        insert_membership(&handler, group_1, "patrick").await;
+        insert_membership(&handler, group_2, "patrick").await;
         let mut bob_groups = HashSet::new();
         bob_groups.insert("Group1".to_string());
         let mut patrick_groups = HashSet::new();
diff --git a/src/infra/tcp_backend_handler.rs b/src/infra/tcp_backend_handler.rs
index 1f869c7..1c2009f 100644
--- a/src/infra/tcp_backend_handler.rs
+++ b/src/infra/tcp_backend_handler.rs
@@ -29,6 +29,7 @@ mockall::mock! {
         async fn get_user_groups(&self, user: String) -> DomainResult<HashSet<String>>;
         async fn create_user(&self, request: CreateUserRequest) -> DomainResult<()>;
         async fn create_group(&self, request: CreateGroupRequest) -> DomainResult<i32>;
+        async fn add_user_to_group(&self, request: AddUserToGroupRequest) -> DomainResult<()>;
     }
     #[async_trait]
     impl TcpBackendHandler for TestTcpBackendHandler {