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POST
/
api
/
auth
/
signin
Sign In
curl --request POST \
  --url https://api.example.com/api/auth/signin \
  --header 'Content-Type: application/json' \
  --data '
{
  "email": "<string>",
  "password": "<string>"
}
'
{
  "Location": {},
  "Set-Cookie": {},
  "sb-access-token": {},
  "sb-refresh-token": {},
  "Retry-After": {}
}

​
Overview

This endpoint authenticates an existing user using their email and password with Supabase Authentication. Upon successful login, the user receives session tokens and is redirected to the homepage.

​
Authentication

This endpoint does not require prior authentication (it creates the authentication session).

​
Rate Limiting

This endpoint is protected by rate limiting middleware:
  • Default limit: 100 requests per 60 seconds
  • Returns 429 Too Many Requests when limit is exceeded
  • Prevents brute force attacks

​
Request Body

This endpoint accepts application/x-www-form-urlencoded form data (typically from an HTML form submission).
​
email
string
required
User’s registered email address.Example: user@example.com
​
password
string
required
User’s password.Example: SecurePass123!

​
Response

Upon successful authentication, this endpoint redirects to the homepage (/) with a 302 Found status code.
The redirect response includes:
​
Location
header
Redirect URL: /
​
Set-Cookie
header
Session cookies containing authentication tokens

​
Cookies Set

Upon successful sign-in, the following HTTP-only cookies are automatically set:
​
sb-access-token
cookie
Attributes: HttpOnly, Secure, SameSite=Lax, Max-Age=7 daysContains the Supabase access token for authenticated requests
​
sb-refresh-token
cookie
Attributes: HttpOnly, Secure, SameSite=Lax, Max-Age=7 daysContains the Supabase refresh token to maintain the session

​
Example Request

curl -X POST "https://anidev.vercel.app/api/auth/signin" \
  -H "Content-Type: application/x-www-form-urlencoded" \
  -d "email=user@example.com&password=SecurePass123!" \
  -L \
  -c cookies.txt

​
Success Response

Status Code: 302 Found (Redirect) Headers: 
Location: /
Set-Cookie: sb-access-token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...; HttpOnly; Secure; SameSite=Lax; Max-Age=604800; Path=/
Set-Cookie: sb-refresh-token=v1.MRjyg-VNJ8H7zN...; HttpOnly; Secure; SameSite=Lax; Max-Age=604800; Path=/

​
Error Responses

​
Missing Credentials

Status Code: 400 Bad Request 
{
  "error": "Email and password are required",
  "type": "validation"
}

​
Invalid Credentials

Status Code: 401 Unauthorized 
{
  "error": "Invalid email or password",
  "type": "unauthorized"
}

​
Account Not Found

Status Code: 401 Unauthorized 
{
  "error": "No user found with this email",
  "type": "unauthorized"
}

​
Rate Limit Exceeded

Status Code: 429 Too Many Requests 
{
  "error": "Too many requests, please try again later",
  "type": "tooManyRequests"
}
​
Retry-After
header
Number of seconds to wait before making another request

​
Server Error

Status Code: 500 Internal Server Error 
{
  "error": "Internal server error"
}

​
Security Features

Important Security Notes:
  • Passwords are never stored in plain text - Supabase uses secure bcrypt hashing
  • Session tokens are stored in HTTP-only cookies to prevent XSS attacks
  • Cookies use the Secure flag (HTTPS only) in production
  • SameSite=Lax prevents CSRF attacks
  • Rate limiting prevents brute force login attempts
  • Failed login attempts do not reveal whether the email exists

​
Session Management

Once signed in:
  • Access Token: Valid for 1 hour by default
  • Refresh Token: Valid for 7 days (matches cookie max-age)
  • Auto-Refresh: The client should implement token refresh logic before expiration
  • Cookie Expiry: Cookies expire after 7 days, requiring re-authentication

​
Handling Authentication State

// Check if user is authenticated
const checkAuth = async () => {
  try {
    const response = await fetch('/api/auth/session', {
      credentials: 'include'
    });
    
    if (response.ok) {
      const session = await response.json();
      return session.user;
    }
  } catch (err) {
    console.error('Not authenticated');
  }
  return null;
};

// Use in your app
const user = await checkAuth();
if (!user) {
  // Redirect to sign in page
  window.location.href = '/signin';
}

​
Redirect Behavior

Default Redirect: After successful sign-in, users are redirected to / (homepage).To customize the redirect destination, you can:
  1. Add a redirect query parameter to the form action
  2. Modify the endpoint to accept a returnTo parameter
  3. Store the intended destination in session storage before redirecting to sign-in

​
Form Integration Example

---
// signin.astro
const error = Astro.url.searchParams.get('error');
---

<form action="/api/auth/signin" method="POST">
  <input 
    type="email" 
    name="email" 
    placeholder="Email" 
    required 
  />
  <input 
    type="password" 
    name="password" 
    placeholder="Password" 
    required 
  />
  
  {error && <p class="error">{error}</p>}
  
  <button type="submit">Sign In</button>
  
  <p>
    Don't have an account? 
    <a href="/signup">Sign up</a>
  </p>
</form>
  • Sign Up - Create a new user account
  • Sign Out - End the current session
  • Session - Check current authentication status
  • Get Profile - Retrieve authenticated user’s profile