add authentication with next-auth

dashboard-app-course/auth.ts

@@ -0,0 +1,42 @@
+import NextAuth from 'next-auth';
+import { authConfig } from './auth.config';
+import Credentials from 'next-auth/providers/credentials';
+import { z } from 'zod';
+import type { User } from '@/app/lib/definitions';
+import bcrypt from 'bcrypt';
+import postgres from 'postgres';
+ 
+const sql = postgres(process.env.POSTGRES_URL!, { ssl: 'require' });
+
+async function getUser(email: string): Promise<User | undefined> {
+    try{
+        const user = await sql<User[]>`SELECT * FROM users WHERE email=${email}`;
+        return user[0];
+    } catch(error){
+        console.error('Failed to fetch user:', error);
+        throw new Error('Failed to fetch user.');
+    }
+}
+
+export const { auth, signIn, signOut } = NextAuth({
+  ...authConfig,
+  providers: [Credentials({
+    async authorize(credentials){
+        const parsedCredentials = z
+        .object({ email: z.string().email(), password: z.string().min(6)})
+        .safeParse(credentials);
+
+        if(parsedCredentials.success){
+            const { email, password } = parsedCredentials.data;
+            const user = await getUser(email);
+            if(!user) return null;
+            const passwordsMatch = await bcrypt.compare(password, user.password);
+
+            if(passwordsMatch) return user;
+        }
+        
+        console.log('Invalid credentials');
+        return null;
+    },
+  })],
+});