Update docs. Implemented a one-time token to work around domain cookies not being immediately return by the browser. Reduce db queries on /api/verify requests.

2025-10-28 08:20:12 +11:00
parent da6fd5b800
commit 7074242907
5 changed files with 183 additions and 37 deletions
--- a/docs/forward-auth.md
+++ b/docs/forward-auth.md
@@ -1,9 +1,5 @@
 # Forward Authentication

-References:
- https://www.reddit.com/r/selfhosted/comments/1hybe81/i_wanted_to_implement_my_own_forward_auth_proxy/
- https://www.kevinsimper.dk/posts/implementing-a-forward_auth-proxy-tips-and-details
-
 ## Overview

 Forward authentication allows a reverse proxy (like Caddy, Nginx, Traefik) to delegate authentication decisions to a separate service. Clinch implements this pattern to provide SSO for multiple applications.
@@ -22,7 +18,7 @@ login_params = {
 login_url = "#{base_url}/signin?#{login_params.to_query}"
 ```

-Example: `https://clinch.aapamilne.com/signin?rd=https://metube.aapamilne.com/&rm=GET`
+Example: `https://clinch.example.com/signin?rd=https://metube.example.com/&rm=GET`

 ### Tip 2: Root Domain Cookies ✅

@@ -30,7 +26,7 @@ Clinch sets authentication cookies on the root domain to enable cross-subdomain

 ```ruby
 def extract_root_domain(host)
-  # clinch.aapamilne.com -> .aapamilne.com
+  # clinch.example.com -> .example.com
  # app.example.co.uk -> .example.co.uk
  # localhost -> nil (no domain restriction)
 end
@@ -40,14 +36,73 @@ cookies.signed.permanent[:session_id] = {
  httponly: true,
  same_site: :lax,
  secure: Rails.env.production?,
-  domain: ".aapamilne.com"  # Available to all subdomains
+  domain: ".example.com"  # Available to all subdomains
 }
 ```

 This allows the same session cookie to work across:
- `clinch.aapamilne.com` (auth service)
- `metube.aapamilne.com` (protected app)
- `sonarr.aapamilne.com` (protected app)
+- `clinch.example.com` (auth service)
+- `metube.example.com` (protected app)
+- `sonarr.example.com` (protected app)
+
+### Tip 3: Race Condition Solution with One-Time Tokens ✅
+
+**Problem**: After successful authentication, there's a race condition where the browser immediately follows the redirect to the protected application, but the reverse proxy makes a forward auth request before the browser has processed and started sending the new session cookie.
+
+**Solution**: Clinch uses a one-time token system to bridge this timing gap:
+
+```ruby
+# During authentication (authentication.rb)
+def create_forward_auth_token(session_obj)
+  token = SecureRandom.urlsafe_base64(32)
+
+  # Store token for 30 seconds
+  Rails.cache.write("forward_auth_token:#{token}", session_obj.id, expires_in: 30.seconds)
+
+  # Add token to redirect URL
+  if session[:return_to_after_authenticating].present?
+    original_url = session[:return_to_after_authenticating]
+    uri = URI.parse(original_url)
+    query_params = URI.decode_www_form(uri.query || "").to_h
+    query_params['fa_token'] = token
+    uri.query = URI.encode_www_form(query_params)
+    session[:return_to_after_authenticating] = uri.to_s
+  end
+end
+```
+
+```ruby
+# In forward auth verification (forward_auth_controller.rb)
+def check_forward_auth_token
+  token = params[:fa_token]
+  return nil unless token.present?
+
+  session_id = Rails.cache.read("forward_auth_token:#{token}")
+  return nil unless session_id
+
+  session = Session.find_by(id: session_id)
+  return nil unless session && !session.expired?
+
+  # Delete token immediately (one-time use)
+  Rails.cache.delete("forward_auth_token:#{token}")
+
+  Rails.logger.info "ForwardAuth: Valid one-time token used for session #{session_id}"
+  session_id
+end
+```
+
+**How it works:**
+1. User authenticates → Rails sets session cookie + generates one-time token
+2. Token gets appended to redirect URL: `https://metube.example.com/?fa_token=abc123...`
+3. Browser follows redirect → Caddy makes forward auth request with token
+4. Forward auth validates token → authenticates user immediately
+5. Token is deleted (one-time use) → subsequent requests use normal cookies
+
+**Security Features:**
+- Tokens expire after 30 seconds
+- One-time use (deleted after validation)
+- Secure random generation
+- Session validation before token acceptance

 ## Authelia Analysis

@@ -67,14 +122,20 @@ This allows the same session cookie to work across:

 ### Authentication Flow

-1. **User visits** `https://metube.aapamilne.com/`
-2. **Caddy forwards** to `http://clinch:9000/api/verify?rd=https://clinch.aapamilne.com`
+1. **User visits** `https://metube.example.com/`
+2. **Caddy forwards** to `http://clinch:9000/api/verify?rd=https://clinch.example.com`
 3. **Clinch checks session**:
   - **If authenticated**: Returns `200 OK` with user headers
   - **If not authenticated**: Returns `302 Found` to login URL with redirect parameters
 4. **Browser follows redirect** to Clinch login page
-5. **User logs in** → gets redirected back to original MEtube URL
-6. **Caddy tries again** → succeeds and forwards to MEtube
+5. **User logs in** (with TOTP if enabled):
+   - Rails creates session and sets cross-domain cookie
+   - **Rails generates one-time token** and appends to redirect URL
+   - User is redirected to: `https://metube.example.com/?fa_token=abc123...`
+6. **Browser follows redirect** → Caddy makes forward auth request with token
+7. **Clinch validates one-time token** → authenticates user immediately
+8. **Token is deleted** → subsequent requests use normal session cookies
+9. **Caddy forwards to MEtube** with proper authentication headers

 ### Response Headers

@@ -88,21 +149,21 @@ Remote-Admin: false

 **Redirect to Login (302 Found):**
 ```
-Location: https://clinch.aapamilne.com/signin?rd=https://metube.aapamilne.com/&rm=GET
+Location: https://clinch.example.com/signin?rd=https://metube.example.com/&rm=GET
 ```

 ## Caddy Configuration

 ```caddyfile
 # Clinch SSO (main authentication server)
-clinch.aapamilne.com {
+clinch.example.com {
    reverse_proxy clinch:9000
 }

 # MEtube (protected by Clinch)
-metube.aapamilne.com {
+metube.example.com {
    forward_auth clinch:9000 {
-        uri /api/verify?rd=https://clinch.aapamilne.com
+        uri /api/verify?rd=https://clinch.example.com
        copy_headers Remote-User Remote-Email Remote-Groups Remote-Admin
    }

@@ -126,7 +187,7 @@ metube.aapamilne.com {

 ```bash
 # Test forward auth endpoint directly
-curl -v http://localhost:9000/api/verify?rd=https://clinch.aapamilne.com
+curl -v http://localhost:9000/api/verify?rd=https://clinch.example.com

 # Should return 302 redirect to login page
 # Or 200 OK if you have a valid session cookie
@@ -139,6 +200,10 @@ curl -v http://localhost:9000/api/verify?rd=https://clinch.aapamilne.com
 1. **Authentication Loop**: Check that cookies are set on the root domain
 2. **Session Not Shared**: Verify `extract_root_domain` is working correctly
 3. **Caddy Connection**: Ensure `clinch:9000` resolves from your Caddy container
+4. **Race Condition After Authentication**:
+   - **Problem**: Forward auth fails immediately after login due to cookie timing
+   - **Solution**: One-time tokens automatically bridge this gap
+   - **Debug**: Look for "ForwardAuth: Valid one-time token used" in logs

 ### Debug Logging

@@ -146,8 +211,21 @@ Enable debug logging in `forward_auth_controller.rb` to see:
 - Headers received from Caddy
 - Domain extraction results
 - Redirect URLs being generated
+- Token validation during race condition resolution

 ```ruby
 Rails.logger.info "ForwardAuth Headers: Host=#{host}, X-Forwarded-Host=#{original_host}"
 Rails.logger.info "Setting 302 redirect to: #{login_url}"
-```
+Rails.logger.info "ForwardAuth: Valid one-time token used for session #{session_id}"
+Rails.logger.info "Authentication: Added forward auth token to redirect URL: #{url}"
+```
+
+**Key log messages to watch for:**
+- `"Authentication: Added forward auth token to redirect URL"` - Token generation during login
+- `"ForwardAuth: Valid one-time token used for session X"` - Successful race condition resolution
+- `"ForwardAuth: Session cookie present: false"` - Cookie timing issue (should be resolved by token)
+
+## Other References
+
+- https://www.reddit.com/r/selfhosted/comments/1hybe81/i_wanted_to_implement_my_own_forward_auth_proxy/
+- https://www.kevinsimper.dk/posts/implementing-a-forward_auth-proxy-tips-and-details