CORS configuration in Supabase

Introduction

CORS configuration lets your web app safely ask for data from your Supabase backend even if they are on different websites.

When your frontend app runs on a different website than your Supabase backend.

When you want to allow only certain websites to access your Supabase data.

When you want to prevent other websites from using your Supabase API without permission.

Syntax

Supabase

cors:
  allowed_origins:
    - 'https://example.com'
    - 'https://another-site.com'
  allowed_methods:
    - GET
    - POST
  allowed_headers:
    - Content-Type
    - Authorization

allowed_origins is a list of website addresses allowed to access your backend.

You can specify which HTTP methods and headers are allowed for security.

Examples

Allow only https://myapp.com to access your Supabase backend.

Supabase

cors:
  allowed_origins:
    - 'https://myapp.com'

Allow any website to access your backend (less secure, use carefully).

Supabase

cors:
  allowed_origins:
    - '*'

Allow two specific sites with GET and POST methods and only Authorization header.

Supabase

cors:
  allowed_origins:
    - 'https://site1.com'
    - 'https://site2.com'
  allowed_methods:
    - GET
    - POST
  allowed_headers:
    - Authorization

Sample Program

This configuration allows only https://myfrontend.com to call your Supabase backend using GET and POST requests. It also allows the headers Content-Type and Authorization for these requests.

Supabase

cors:
  allowed_origins:
    - 'https://myfrontend.com'
  allowed_methods:
    - GET
    - POST
  allowed_headers:
    - Content-Type
    - Authorization

Important Notes

Always restrict allowed_origins to trusted websites to keep your backend safe.

Using '*' for origins allows any website but can expose your backend to risks.

Test your CORS settings by trying to access your backend from different websites.

Summary

CORS controls which websites can talk to your Supabase backend.

Set allowed origins, methods, and headers to keep your data safe.

Use specific origins instead of '*' for better security.

Practice

1. What does CORS configuration in Supabase control?

easy

A. How fast your database queries run

B. Which websites can access your Supabase backend

C. The color scheme of your Supabase dashboard

D. The size of your database storage

Solution

1. Step 1: Understand CORS purpose

   CORS stands for Cross-Origin Resource Sharing and controls which websites can send requests to your backend.

2. Step 2: Apply to Supabase context

   In Supabase, CORS settings define allowed origins that can communicate with your backend securely.

3. Final Answer:

   Which websites can access your Supabase backend -> Option B

4. Quick Check:

   CORS controls access origins [OK]

Hint: CORS controls website access to backend [OK]

Common Mistakes:

• Confusing CORS with database speed
• Thinking CORS changes UI colors
• Assuming CORS affects storage size

2. Which of the following is the correct way to allow only https://example.com in Supabase CORS settings?

easy

A. Set allowed origins to ['https://example.com']

B. Set allowed origins to ['http://example.com']

C. Set allowed origins to ['*']

D. Set allowed origins to ['example.com']

Solution

1. Step 1: Understand allowed origins format

   Allowed origins must include the full scheme (https://) and domain to be valid.

2. Step 2: Match correct origin

   Only 'https://example.com' matches the requirement exactly; '*' allows all origins, which is insecure.

3. Final Answer:

   Set allowed origins to ['https://example.com'] -> Option A

4. Quick Check:

   Use full URL with https [OK]

Hint: Use full URL with https:// for origins [OK]

Common Mistakes:

• Using '*' which allows all origins
• Omitting https:// in origin
• Using only domain without scheme

3. Given this Supabase CORS config: { allowedOrigins: ['https://app.com'], allowedMethods: ['GET', 'POST'] }, what happens if a browser sends a DELETE request from https://app.com?

medium

A. Request is allowed but logged as warning

B. Request is allowed and processed

C. Request is blocked due to origin not allowed

D. Request is blocked due to method not allowed

Solution

1. Step 1: Check allowed origins

   The origin 'https://app.com' is allowed, so origin is not the issue.

2. Step 2: Check allowed methods

   Only 'GET' and 'POST' methods are allowed; 'DELETE' is not permitted.

3. Final Answer:

   Request is blocked due to method not allowed -> Option D

4. Quick Check:

   Method not in allowedMethods [OK]

Hint: Check if method is in allowedMethods list [OK]

Common Mistakes:

• Assuming origin blocks the request
• Thinking DELETE is allowed by default
• Believing request is allowed with warning

4. You configured Supabase CORS with allowedOrigins: ['https://myapp.com'] but your frontend at https://myapp.com still gets CORS errors. What is the likely mistake?

medium

A. You forgot to include 'https://' in allowedOrigins

B. You set allowedOrigins to '*' instead of specific origin

C. You did not add the frontend URL exactly as it appears

D. You need to add 'http://' instead of 'https://'

Solution

1. Step 1: Verify exact origin match

   CORS requires exact match including scheme, domain, and port if any.

2. Step 2: Check frontend URL correctness

   If frontend URL differs (e.g., with www or port), it must be added exactly in allowedOrigins.

3. Final Answer:

   You did not add the frontend URL exactly as it appears -> Option C

4. Quick Check:

   Exact origin match needed [OK]

Hint: Match frontend URL exactly in allowedOrigins [OK]

Common Mistakes:

• Assuming '*' fixes errors
• Using http instead of https incorrectly
• Ignoring subdomains or ports in origin

5. You want to securely allow your React app at https://app.example.com and your admin panel at https://admin.example.com to access Supabase. Which CORS configuration is best?

hard

A. allowedOrigins: ['https://app.example.com', 'https://admin.example.com']

B. allowedOrigins: ['*']

C. allowedOrigins: ['https://example.com']

D. allowedOrigins: ['http://app.example.com', 'http://admin.example.com']

Solution

1. Step 1: Avoid using '*' for security

   Using '*' allows all origins, which is insecure for private apps.

2. Step 2: Specify exact allowed origins

   List both 'https://app.example.com' and 'https://admin.example.com' to allow only these trusted sites.

3. Step 3: Use correct scheme https

   Use 'https://' to match secure frontend URLs exactly.

4. Final Answer:

   allowedOrigins: ['https://app.example.com', 'https://admin.example.com'] -> Option A

5. Quick Check:

   List exact secure origins [OK]

Hint: List each allowed origin explicitly with https [OK]

Common Mistakes:

• Using '*' which is insecure
• Using only base domain without subdomains
• Using http instead of https