go-loose/docs/client-login.md

Client application login

Go Loose can host login for browser-facing Go applications. Your application never handles the user's IdP password. It redirects the browser to Go Loose, receives a short-lived one-time authorization code, exchanges that code from its backend using a client secret, and stores the returned opaque session in an HTTP-only cookie.

1. Configure the application in Go Loose

1. Open Applications and choose Configure client login.
2. Add the exact callback URL, for example https://nmbs.guess.local/auth/callback.
3. Save and copy the client secret. It is shown once.
4. Open Users, invite the user by the email returned by the IdP, and choose Manage to grant access to the application.

The invitation requires an initial password. Tenant login hosts accept database credentials only; SSO is reserved for system administration on the bare authentication domain.

Saving client configuration rotates the secret. Callback URLs require HTTPS, except localhost and 127.0.0.1 while Go Loose development login is enabled.

2. Add the Go client

go get github.com/danyel/go-loose/client

Configure the hosted login and register its handlers:

package main

import (
	"fmt"
	"log"
	"net/http"
	"os"
	"time"

	goloose "github.com/danyel/go-loose/client"
)

func main() {
	auth, err := goloose.NewBrowserAuth(goloose.BrowserAuthConfig{
		BaseURL:        "https://nmbs.auth.example.com",
		ClientID:       os.Getenv("GO_LOOSE_CLIENT_ID"),
		ClientSecret:   os.Getenv("GO_LOOSE_CLIENT_SECRET"),
		RedirectURL:    "https://nmbs.guess.local/auth/callback",
		AfterLoginURL:  "/app",
		AfterLogoutURL: "/",
		LoginPath:      "/login",
		CookieSecure:   true,
		HTTPClient:     &http.Client{Timeout: 3 * time.Second},
	})
	if err != nil {
		log.Fatal(err)
	}

	mux := http.NewServeMux()
	mux.HandleFunc("GET /login", auth.LoginHandler)
	mux.HandleFunc("GET /auth/callback", auth.CallbackHandler)
	mux.HandleFunc("POST /logout", auth.LogoutHandler)

	protected := auth.Middleware(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		user, ok := goloose.UserFromContext(r.Context())
		if !ok {
			http.Error(w, "user missing", http.StatusInternalServerError)
			return
		}
		fmt.Fprintf(w, "Hello %s from tenant %s", user.DisplayName, user.TenantSlug)
	}))
	mux.Handle("GET /app", protected)
	mux.Handle("GET /api/profile", protected)

	log.Fatal(http.ListenAndServe(":8090", mux))
}

Keep GO_LOOSE_CLIENT_SECRET in a secret manager, never source control. In local development, configure an exact callback such as http://localhost:8090/auth/callback and set CookieSecure: false.

Tenant login hostname

Each tenant has its own login origin:

https://<tenant-slug>.<GO_LOOSE_AUTH_DOMAIN>

For tenant nmbs with GO_LOOSE_AUTH_DOMAIN=auth.dev, configure the Go client with:

BaseURL: "http://nmbs.auth.dev:18080"

For local development, add the tenant hostname to /etc/hosts:

127.0.0.1 nmbs.auth.dev

Production should configure wildcard DNS and TLS for *.auth.example.com, route those hosts to Go Loose, and use:

GO_LOOSE_BASE_URL=https://auth.example.com
GO_LOOSE_AUTH_DOMAIN=auth.example.com
GO_LOOSE_OIDC_REDIRECT_URL=https://auth.example.com/auth/callback

The client package initially redirects to /connect/authorize. Go Loose verifies the registered client and exact callback, canonicalizes the browser onto the tenant hostname, and renders <Tenant name> login for the requested application.

3. Browser flow

Browser → GET /login on client application
        → GET /connect/authorize on Go Loose
        → separate Go Loose client login
        → organization OIDC provider
        → Go Loose validates user + application grant
        → client /auth/callback?code=...&state=...
Client  → POST /connect/token with Authorization: Basic <client-id:secret>
        ← opaque 12-hour session token
Browser ← HTTP-only SameSite session cookie on client application
Request → client middleware → GET /connect/userinfo → protected handler
                                      Authorization: Bearer <opaque-session>

The authorization code expires after two minutes and can be used once. Redirect URIs must match exactly. Removing a user's application grant immediately makes /connect/userinfo reject existing sessions. Logout revokes the central session and clears the local cookie.

Security and availability

• Use TLS for both Go Loose and the client application.
• Keep client secrets server-side and rotate them after suspected disclosure.
• Do not replace the middleware's fail-closed behavior with an allow-on-error fallback.
• Apply CSRF protection to state-changing routes in the client application; the package handles login state, not your application forms.
• The middleware checks Go Loose on every request for immediate revocation. Deploy Go Loose highly available and use a bounded HTTP timeout.
• API-key authentication and browser-user authentication are independent. Use client.Middleware for service/API keys and BrowserAuth.Middleware for logged-in users.

Troubleshooting 403

403 your account does not have access to this application means authentication succeeded but the user lacks an application grant. In Go Loose, open Users, select the user, choose Manage, and enable the target application. A missing or incorrect token header returns 401, not 403.