Email/password authentication in Supabase - Mini Project: Build & Apply

Email/password authentication

📖 Scenario: You are building a simple web app that lets users sign up and log in using their email and password. You will use Supabase, a cloud service that manages user accounts securely for you.

🎯 Goal: Create a Supabase project setup that enables email/password authentication. You will write code to initialize the Supabase client, and implement sign-up and sign-in functions.

📋 What You'll Learn

Initialize Supabase client with URL and anon key

Write a function to sign up users with email and password

Write a function to sign in users with email and password

💡 Why This Matters

🌍 Real World

Email/password authentication is a common way to let users securely create accounts and log in to web apps without managing passwords yourself.

💼 Career

Understanding how to set up authentication with cloud services like Supabase is essential for backend and full-stack developers building user-facing applications.

1

Initialize Supabase client

Create a constant called supabaseUrl with the value "https://xyzcompany.supabase.co" and a constant called supabaseAnonKey with the value "public-anonymous-key". Then create a constant called supabase by calling createClient(supabaseUrl, supabaseAnonKey).

Supabase

# Create constants supabaseUrl and supabaseAnonKey with the given values
# Then create supabase client using createClient
# Your code here

Hint

Use const to declare variables. The createClient function takes the URL and anon key as arguments.

2

Write sign-up function

Write an async function called signUpUser that takes email and password as parameters. Inside, call supabase.auth.signUp({ email, password }) and return the result.

Supabase

import { createClient } from '@supabase/supabase-js';

const supabaseUrl = "https://xyzcompany.supabase.co";
const supabaseAnonKey = "public-anonymous-key";
const supabase = createClient(supabaseUrl, supabaseAnonKey);

// Write async function signUpUser(email, password) to sign up users
# Your code here

Hint

Use async function and await the signUp call with the email and password parameters.

3

Write sign-in function

Write an async function called signInUser that takes email and password as parameters. Inside, call supabase.auth.signInWithPassword({ email, password }) and return the result.

Supabase

import { createClient } from '@supabase/supabase-js';

const supabaseUrl = "https://xyzcompany.supabase.co";
const supabaseAnonKey = "public-anonymous-key";
const supabase = createClient(supabaseUrl, supabaseAnonKey);

async function signUpUser(email, password) {
    return await supabase.auth.signUp({ email, password });
}

// Write async function signInUser(email, password) to sign in users
# Your code here

Hint

Use async function and await the signInWithPassword call with the email and password parameters.

Practice

1. What is the primary purpose of using signUp in Supabase email/password authentication?

easy

A. To register a new user with email and password

B. To log in an existing user

C. To reset a user's password

D. To delete a user account

Solution

1. Step 1: Understand the function of signUp

   The signUp method is used to create a new user account with an email and password.

2. Step 2: Differentiate from other authentication methods

   Logging in uses signInWithPassword, not signUp. Password reset and deletion are separate actions.

3. Final Answer:

   To register a new user with email and password -> Option A

4. Quick Check:

   signUp = register new user [OK]

Hint: Remember: signUp means create account, not login [OK]

Common Mistakes:

• Confusing signUp with signInWithPassword
• Thinking signUp resets passwords
• Assuming signUp deletes accounts

2. Which of the following is the correct syntax to sign in a user with email and password using Supabase?

easy

A. supabase.auth.login({ email: '[e-mail]', password: 'pass123' })

B. supabase.auth.signInWithPassword({ email: '[e-mail]', password: 'pass123' })

C. supabase.auth.signUp({ email: '[e-mail]', password: 'pass123' })

D. supabase.auth.authenticate({ email: '[e-mail]', password: 'pass123' })

Solution

1. Step 1: Identify the correct method for signing in

   The method to sign in with email and password is signInWithPassword.

2. Step 2: Check the syntax format

   The correct syntax uses an object with email and password keys inside signInWithPassword.

3. Final Answer:

   supabase.auth.signInWithPassword({ email: '[e-mail]', password: 'pass123' }) -> Option B

4. Quick Check:

   signInWithPassword = login syntax [OK]

Hint: signInWithPassword is for login, signUp is for registration [OK]

Common Mistakes:

• Using signUp instead of signInWithPassword to login
• Using non-existent methods like login or authenticate
• Incorrect object structure in method call

3. What will be the result of this code snippet?

const { data, error } = await supabase.auth.signUp({ email: '[e-mail]', password: '123' });
console.log(error ? error.message : 'User created');

medium

A. Password should be at least 6 characters

B. User created

C. Email already exists

D. SyntaxError

Solution

1. Step 1: Analyze the password length

   The password '123' is only 3 characters, which is too short for Supabase's minimum password length (usually 6).

2. Step 2: Understand error handling

   The error object will contain a message about the weak password, so the console logs that message.

3. Final Answer:

   Password should be at least 6 characters -> Option A

4. Quick Check:

   Short password triggers error message [OK]

Hint: Passwords must meet minimum length to avoid errors [OK]

Common Mistakes:

• Assuming user is created with short password
• Ignoring error object and expecting success
• Confusing error messages for duplicate email

4. You wrote this code to sign in a user:

const { data, error } = await supabase.auth.signInWithPassword({ email: '[e-mail]' });

Why does it fail and how to fix it?

medium

A. Use signUp instead of signInWithPassword

B. Email format is wrong; fix the email string

C. Missing password field; add password to the object

D. signInWithPassword requires a callback function

Solution

1. Step 1: Check required parameters for signInWithPassword

   The method requires both email and password fields to authenticate.

2. Step 2: Identify missing password

   The code only provides email, so it fails. Adding password fixes the issue.

3. Final Answer:

   Missing password field; add password to the object -> Option C

4. Quick Check:

   Both email and password needed for signInWithPassword [OK]

Hint: Always provide both email and password to signInWithPassword [OK]

Common Mistakes:

• Omitting password when signing in
• Confusing signUp and signInWithPassword usage
• Thinking signInWithPassword needs a callback

5. You want to create a secure signup flow that prevents duplicate emails and weak passwords. Which approach is best?

hard

A. Call signInWithPassword first, then signUp if login fails

B. Allow signup without email verification to speed up user creation

C. Only check password length on client side, skip server validation

D. Use signUp and check error for duplicates or weak passwords before confirming success

Solution

1. Step 1: Use signUp to register users

   This method handles creating accounts and returns errors for duplicates or weak passwords.

2. Step 2: Check the error object to handle issues

   By checking error, you can inform users about duplicates or weak passwords and prevent bad signups.

3. Final Answer:

   Use signUp and check error for duplicates or weak passwords before confirming success -> Option D

4. Quick Check:

   signUp + error check = secure signup flow [OK]

Hint: Always check errors after signUp to catch duplicates and weak passwords [OK]

Common Mistakes:

• Trying to sign in before signup to check duplicates
• Skipping server-side password validation
• Ignoring email verification importance