Token refresh mechanism in Rest API

Introduction

A token refresh mechanism helps keep users logged in without asking them to sign in again. It safely updates access tokens when they expire.

When a user logs into a website or app and you want to keep them logged in for a long time.

When access tokens expire quickly for security, but you want a smooth user experience.

When you want to avoid asking users to enter their password repeatedly.

When you want to improve security by limiting how long an access token is valid.

When building APIs that require secure, continuous user authentication.

Syntax

Rest API

POST /refresh_token
Headers:
  Authorization: Bearer <refresh_token>
Response:
  {
    "access_token": "new_access_token",
    "expires_in": 3600
  }

The client sends a refresh token to get a new access token.

The server verifies the refresh token and returns a new access token if valid.

Examples

The client sends the refresh token 'abc123refresh' and receives a new access token 'xyz789newtoken'.

Rest API

POST /refresh_token
Authorization: Bearer abc123refresh

Response:
{
  "access_token": "xyz789newtoken",
  "expires_in": 3600
}

If the refresh token is expired or invalid, the server returns an error.

Rest API

POST /refresh_token
Authorization: Bearer expiredtoken

Response:
{
  "error": "invalid_refresh_token"
}

Sample Program

This simple Flask app shows how a refresh token is checked and a new access token is returned if valid.

Rest API

from flask import Flask, request, jsonify
import time

app = Flask(__name__)

# Simulated storage for refresh tokens
refresh_tokens = {
    "valid_refresh_token": {
        "user_id": 1,
        "expires_at": time.time() + 3600
    }
}

@app.route('/refresh_token', methods=['POST'])
def refresh_token():
    auth_header = request.headers.get('Authorization')
    if not auth_header or not auth_header.startswith('Bearer '):
        return jsonify({"error": "missing_token"}), 401

    token = auth_header.split(' ')[1]
    token_data = refresh_tokens.get(token)

    if not token_data or token_data['expires_at'] < time.time():
        return jsonify({"error": "invalid_refresh_token"}), 401

    # Create new access token (here just a dummy string with timestamp)
    new_access_token = f"access_{int(time.time())}"

    return jsonify({
        "access_token": new_access_token,
        "expires_in": 3600
    })

if __name__ == '__main__':
    app.run(debug=False)

Important Notes

Refresh tokens should be stored securely and never exposed to third parties.

Access tokens usually have short life spans; refresh tokens last longer.

Always validate refresh tokens on the server before issuing new access tokens.

Summary

A token refresh mechanism keeps users logged in smoothly by renewing access tokens.

Clients send refresh tokens to get new access tokens without re-entering credentials.

Servers verify refresh tokens and respond with new access tokens or errors.