Replit Install & Auth Skill

Replit Install & Auth

Overview

Set up a Replit App from scratch: configure .replit and replit.nix, manage Secrets (AES-256 encrypted environment variables), and integrate Replit Auth for zero-setup user authentication with Google, GitHub, Apple, X, and Email login.

Prerequisites

Replit account (Free, Core, or Teams plan)
Replit App created from template, GitHub import, or blank
For Auth: deployed app on .replit.app or custom domain

Instructions

Step 1: Configure `.replit` File

# .replit — controls run behavior, deployment, and environment
entrypoint = "index.ts"
run = "npm start"

# Nix modules provide language runtimes
modules = ["nodejs-20:v8-20230920-bd784b9"]

[nix]
channel = "stable-24_05"

[env]
NODE_ENV = "development"
PORT = "3000"

[deployment]
run = ["sh", "-c", "npm start"]
deploymentTarget = "autoscale"
build = ["sh", "-c", "npm run build"]
ignorePorts = [3001]

[unitTest]
language = "nodejs"

[packager]
language = "nodejs"
  [packager.features]
  packageSearch = true
  guessImports = true

[gitHubImport]
requiredFiles = [".replit", "replit.nix"]

Step 2: Configure `replit.nix`

# replit.nix — system-level dependencies via Nix
{ pkgs }: {
  deps = [
    pkgs.nodejs-20_x
    pkgs.nodePackages.typescript-language-server
    pkgs.nodePackages.pnpm
    pkgs.postgresql
    pkgs.python311
    pkgs.python311Packages.pip
  ];
}

After editing replit.nix, reload the shell for changes to take effect.

Step 3: Configure Secrets

Secrets are encrypted with AES-256 at rest and TLS in transit. Two scopes:

App-level: specific to one Replit App
Account-level: shared across all your Apps

Via UI:
1. Click the lock icon (Secrets) in the left sidebar
2. Add key-value pairs:
   - DATABASE_URL = postgresql://...
   - API_KEY = sk-...
   - JWT_SECRET = your-jwt-secret

Via code — validate at startup:

// src/config.ts
function requireSecrets(keys: string[]): Record<string, string> {
  const missing = keys.filter(k => !process.env[k]);
  if (missing.length > 0) {
    console.error(`Missing secrets: ${missing.join(', ')}`);
    console.error('Add them in the Secrets tab (lock icon in sidebar)');
    process.exit(1);
  }
  return Object.fromEntries(keys.map(k => [k, process.env[k]!]));
}

const config = requireSecrets(['DATABASE_URL', 'JWT_SECRET']);

Secrets sync automatically between Workspace and Deployments. Replit's Secret Scanner warns if you paste API keys directly into code files.

Step 4: Add Replit Auth

Replit Auth provides zero-setup authentication. Users log in with Google, GitHub, Apple, X, or Email. Replit handles sessions via cookies, password resets, and user management.

Express.js integration:

// src/auth.ts
import express from 'express';

const app = express();

// Replit Auth injects these headers on authenticated requests
interface ReplitUser {
  id: string;        // X-Replit-User-Id
  name: string;      // X-Replit-User-Name
  bio: string;       // X-Replit-User-Bio
  url: string;       // X-Replit-User-Url
  image: string;     // X-Replit-User-Profile-Image
  roles: string;     // X-Replit-User-Roles
  teams: string;     // X-Replit-User-Teams
}

function getReplitUser(req: express.Request): ReplitUser | null {
  const id = req.headers['x-replit-user-id'] as string;
  if (!id) return null;
  return {
    id,
    name: req.headers['x-replit-user-name'] as string,
    bio: req.headers['x-replit-user-bio'] as string,
    url: req.headers['x-replit-user-url'] as string,
    image: req.headers['x-replit-user-profile-image'] as string,
    roles: req.headers['x-replit-user-roles'] as string,
    teams: req.headers['x-replit-user-teams'] as string,
  };
}

// Auth middleware
function requireAuth(req: express.Request, res: express.Response, next: express.NextFunction) {
  const user = getReplitUser(req);
  if (!user) return res.status(401).json({ error: 'Not authenticated' });
  (req as any).user = user;
  next();
}

// Client-side: GET /__replauthuser returns current user info
// Login: direct user to Replit's login page for your app

Flask integration:

from flask import Flask, request, jsonify

app = Flask(__name__)

def get_replit_user():
    user_id = request.headers.get('X-Replit-User-Id')
    if not user_id:
        return None
    return {
        'id': user_id,
        'name': request.headers.get('X-Replit-User-Name', ''),
        'roles': request.headers.get('X-Replit-User-Roles', ''),
        'teams': request.headers.get('X-Replit-User-Teams', ''),
        'image': request.headers.get('X-Replit-User-Profile-Image', ''),
    }

@app.route('/api/profile')
def profile():
    user = get_replit_user()
    if not user:
        return jsonify({'error': 'Not authenticated'}), 401
    return jsonify(user)

Step 5: Verify Setup

// test-setup.ts — run to verify everything works
const checks = {
  nix: process.version,  // should show Node version
  secrets: !!process.env.DATABASE_URL,
  replSlug: process.env.REPL_SLUG,
  replOwner: process.env.REPL_OWNER,
  replId: process.env.REPL_ID,
};
console.log('Replit Setup Verification:', checks);

Built-in environment variables available in every Repl: | Variable | Description | |----------|-------------| | REPL_SLUG | Your Repl's name/slug | | REPL_OWNER | Owner username | | REPL_ID | Unique Repl identifier | | REPL_IDENTITY | PASETO token signed by Replit infra | | REPLIT_DB_URL | Key-value database endpoint |

Error Handling

| Error | Cause | Solution | |-------|-------|----------| | Module not found | Nix package missing | Add to replit.nix deps, reload shell | | EACCES permission | Wrong file permissions | Check .replit run command syntax | | Secret undefined | Not set in Secrets tab | Add via sidebar lock icon | | Auth headers empty | Not deployed / local dev | Auth only works on deployed .replit.app URLs | | channel not found | Invalid Nix channel | Use stable-24_05 or check Nix channels list |

Resources

Next Steps

Proceed to replit-hello-world for a working starter app, or replit-deploy-integration to deploy.

Agent Skills: Replit Install & Auth

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