B2B-88: add starter kit structure and elements

packages/supabase/src/hooks/use-sign-in-with-email-password.ts

@@ -0,0 +1,30 @@
+import type { SignInWithPasswordCredentials } from '@supabase/supabase-js';
+
+import { useMutation } from '@tanstack/react-query';
+
+import { useSupabase } from './use-supabase';
+
+export function useSignInWithEmailPassword() {
+  const client = useSupabase();
+  const mutationKey = ['auth', 'sign-in-with-email-password'];
+
+  const mutationFn = async (credentials: SignInWithPasswordCredentials) => {
+    const response = await client.auth.signInWithPassword(credentials);
+
+    if (response.error) {
+      throw response.error.message;
+    }
+
+    const user = response.data?.user;
+    const identities = user?.identities ?? [];
+
+    // if the user has no identities, it means that the email is taken
+    if (identities.length === 0) {
+      throw new Error('User already registered');
+    }
+
+    return response.data;
+  };
+
+  return useMutation({ mutationKey, mutationFn });
+}