feat(proxy): add /auth/token and /auth/refresh endpoints (#18)

Closes homelab#6 (P3.1) and homelab#8 (P3.3)

## Endpoints

| Path | Method | Body | What it does |
|------|--------|------|-------------|
| `/auth/token` | POST | `{username, password, scope?}` | Password grant → JWT |
| `/auth/refresh` | POST | `{refresh_token, scope?}` | Refresh grant → new JWT |

Both proxy to Authentik `tokenUrl` (from P3.7 config). Upstream response forwarded verbatim — client sees Authentik errors directly.

internal/proxy/auth_endpoints.go

@@ -0,0 +1,160 @@
+package proxy
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/url"
+	"time"
+
+	"forgejo.riotpiao.com/rock/homelab-frontend/internal/logging"
+)
+
+// tokenRequest is the JSON body for POST /auth/token.
+type tokenRequest struct {
+	Username string `json:"username"`
+	Password string `json:"password"`
+	Scope    string `json:"scope,omitempty"`
+}
+
+// refreshRequest is the JSON body for POST /auth/refresh.
+type refreshRequest struct {
+	RefreshToken string `json:"refresh_token"`
+	Scope        string `json:"scope,omitempty"`
+}
+
+// authClient handles token exchange with the upstream identity provider.
+// Extracted for testability — production uses http.DefaultClient,
+// tests inject a stub.
+type authClient interface {
+	PostForm(url string, data url.Values) (*http.Response, error)
+}
+
+// httpAuthClient wraps http.Client to implement authClient.
+type httpAuthClient struct {
+	client *http.Client
+}
+
+func (c *httpAuthClient) PostForm(url string, data url.Values) (*http.Response, error) {
+	return c.client.PostForm(url, data)
+}
+
+func newAuthClient() authClient {
+	return &httpAuthClient{
+		client: &http.Client{Timeout: 10 * time.Second},
+	}
+}
+
+// handleAuthToken exchanges username+password for a JWT via the upstream
+// identity provider's token endpoint using grant_type=password.
+func (h *Handler) handleAuthToken(w http.ResponseWriter, r *http.Request) {
+	if r.Method != "POST" {
+		writeProblemDetail(w, http.StatusMethodNotAllowed,
+			"about:blank#method-not-allowed", "Method Not Allowed",
+			"POST only", nil)
+		return
+	}
+
+	if h.config.Auth.TokenURL == "" || h.config.Auth.ClientID == "" {
+		writeProblemDetail(w, http.StatusServiceUnavailable,
+			"about:blank#not-configured", "Not Configured",
+			"token endpoint not configured", nil)
+		return
+	}
+
+	var req tokenRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeProblemDetail(w, http.StatusBadRequest,
+			"about:blank#bad-request", "Bad Request",
+			"invalid JSON body", nil)
+		return
+	}
+
+	if req.Username == "" || req.Password == "" {
+		writeProblemDetail(w, http.StatusBadRequest,
+			"about:blank#bad-request", "Bad Request",
+			"username and password are required", nil)
+		return
+	}
+
+	scope := req.Scope
+	if scope == "" {
+		scope = "openid roles permissions"
+	}
+
+	form := url.Values{
+		"grant_type":    {"password"},
+		"username":      {req.Username},
+		"password":      {req.Password},
+		"client_id":     {h.config.Auth.ClientID},
+		"client_secret": {h.config.Auth.ClientSecret},
+		"scope":         {scope},
+	}
+
+	h.forwardTokenResponse(w, form, "/auth/token")
+}
+
+// handleAuthRefresh exchanges a refresh token for a new JWT.
+func (h *Handler) handleAuthRefresh(w http.ResponseWriter, r *http.Request) {
+	if r.Method != "POST" {
+		writeProblemDetail(w, http.StatusMethodNotAllowed,
+			"about:blank#method-not-allowed", "Method Not Allowed",
+			"POST only", nil)
+		return
+	}
+
+	if h.config.Auth.TokenURL == "" || h.config.Auth.ClientID == "" {
+		writeProblemDetail(w, http.StatusServiceUnavailable,
+			"about:blank#not-configured", "Not Configured",
+			"token endpoint not configured", nil)
+		return
+	}
+
+	var req refreshRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeProblemDetail(w, http.StatusBadRequest,
+			"about:blank#bad-request", "Bad Request",
+			"invalid JSON body", nil)
+		return
+	}
+
+	if req.RefreshToken == "" {
+		writeProblemDetail(w, http.StatusBadRequest,
+			"about:blank#bad-request", "Bad Request",
+			"refresh_token is required", nil)
+		return
+	}
+
+	form := url.Values{
+		"grant_type":    {"refresh_token"},
+		"refresh_token": {req.RefreshToken},
+		"client_id":     {h.config.Auth.ClientID},
+		"client_secret": {h.config.Auth.ClientSecret},
+	}
+
+	if req.Scope != "" {
+		form.Set("scope", req.Scope)
+	}
+
+	h.forwardTokenResponse(w, form, "/auth/refresh")
+}
+
+// forwardTokenResponse posts form data to the token endpoint and
+// forwards the response verbatim to the client.
+func (h *Handler) forwardTokenResponse(w http.ResponseWriter, form url.Values, logPath string) {
+	resp, err := h.authHTTP.PostForm(h.config.Auth.TokenURL, form)
+	if err != nil {
+		writeProblemDetail(w, http.StatusBadGateway,
+			"about:blank#bad-gateway", "Bad Gateway",
+			"identity provider unreachable", nil)
+		logging.Errorf("auth upstream error", err, map[string]string{
+			"path": logPath,
+		})
+		return
+	}
+	defer resp.Body.Close()
+
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(resp.StatusCode)
+	io.Copy(w, resp.Body)
+}

internal/proxy/auth_endpoints_test.go

@@ -0,0 +1,315 @@
+package proxy
+
+import (
+	"bytes"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+
+	"forgejo.riotpiao.com/rock/homelab-frontend/internal/config"
+)
+
+// stubAuthClient captures the form data sent and returns a canned response.
+type stubAuthClient struct {
+	lastForm   url.Values
+	statusCode int
+	body       string
+	err        error
+}
+
+func (s *stubAuthClient) PostForm(u string, data url.Values) (*http.Response, error) {
+	s.lastForm = data
+	if s.err != nil {
+		return nil, s.err
+	}
+	return &http.Response{
+		StatusCode: s.statusCode,
+		Body:       io.NopCloser(strings.NewReader(s.body)),
+		Header:     http.Header{"Content-Type": {"application/json"}},
+	}, nil
+}
+
+func newTestHandler(tokenURL, clientID, clientSecret string, client authClient) *Handler {
+	cfg := &config.Config{
+		Auth: config.AuthConfig{
+			TokenURL:     tokenURL,
+			ClientID:     clientID,
+			ClientSecret: clientSecret,
+		},
+	}
+	h := &Handler{
+		config:   cfg,
+		authHTTP: client,
+		routes:   make(map[string]*Route),
+		transports: make(map[string]*http.Transport),
+	}
+	return h
+}
+
+func TestAuthToken_Success(t *testing.T) {
+	stub := &stubAuthClient{
+		statusCode: 200,
+		body:       `{"access_token":"jwt.token.here","refresh_token":"refresh","expires_in":3600}`,
+	}
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", stub)
+
+	body := `{"username":"rock","password":"pass123"}`
+	r := httptest.NewRequest("POST", "/auth/token", strings.NewReader(body))
+	w := httptest.NewRecorder()
+
+	h.handleAuthToken(w, r)
+
+	if w.Code != 200 {
+		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+
+	// Verify form sent to upstream
+	if stub.lastForm.Get("grant_type") != "password" {
+		t.Errorf("grant_type = %q, want password", stub.lastForm.Get("grant_type"))
+	}
+	if stub.lastForm.Get("username") != "rock" {
+		t.Errorf("username = %q, want rock", stub.lastForm.Get("username"))
+	}
+	if stub.lastForm.Get("client_id") != "api-gw" {
+		t.Errorf("client_id = %q, want api-gw", stub.lastForm.Get("client_id"))
+	}
+	if stub.lastForm.Get("client_secret") != "secret" {
+		t.Errorf("client_secret = %q, want secret", stub.lastForm.Get("client_secret"))
+	}
+	if stub.lastForm.Get("scope") != "openid roles permissions" {
+		t.Errorf("scope = %q, want default scope", stub.lastForm.Get("scope"))
+	}
+
+	// Verify response forwarded
+	var resp map[string]interface{}
+	json.NewDecoder(w.Body).Decode(&resp)
+	if resp["access_token"] != "jwt.token.here" {
+		t.Errorf("access_token not forwarded")
+	}
+}
+
+func TestAuthToken_CustomScope(t *testing.T) {
+	stub := &stubAuthClient{statusCode: 200, body: `{}`}
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", stub)
+
+	body := `{"username":"rock","password":"pass","scope":"openid roles"}`
+	r := httptest.NewRequest("POST", "/auth/token", strings.NewReader(body))
+	w := httptest.NewRecorder()
+
+	h.handleAuthToken(w, r)
+
+	if stub.lastForm.Get("scope") != "openid roles" {
+		t.Errorf("scope = %q, want custom scope", stub.lastForm.Get("scope"))
+	}
+}
+
+func TestAuthToken_MissingUsername(t *testing.T) {
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", &stubAuthClient{})
+
+	body := `{"password":"pass"}`
+	r := httptest.NewRequest("POST", "/auth/token", strings.NewReader(body))
+	w := httptest.NewRecorder()
+
+	h.handleAuthToken(w, r)
+
+	if w.Code != 400 {
+		t.Errorf("expected 400, got %d", w.Code)
+	}
+}
+
+func TestAuthToken_MissingPassword(t *testing.T) {
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", &stubAuthClient{})
+
+	body := `{"username":"rock"}`
+	r := httptest.NewRequest("POST", "/auth/token", strings.NewReader(body))
+	w := httptest.NewRecorder()
+
+	h.handleAuthToken(w, r)
+
+	if w.Code != 400 {
+		t.Errorf("expected 400, got %d", w.Code)
+	}
+}
+
+func TestAuthToken_InvalidJSON(t *testing.T) {
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", &stubAuthClient{})
+
+	r := httptest.NewRequest("POST", "/auth/token", strings.NewReader("not json"))
+	w := httptest.NewRecorder()
+
+	h.handleAuthToken(w, r)
+
+	if w.Code != 400 {
+		t.Errorf("expected 400, got %d", w.Code)
+	}
+}
+
+func TestAuthToken_WrongMethod(t *testing.T) {
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", &stubAuthClient{})
+
+	r := httptest.NewRequest("GET", "/auth/token", nil)
+	w := httptest.NewRecorder()
+
+	h.handleAuthToken(w, r)
+
+	if w.Code != 405 {
+		t.Errorf("expected 405, got %d", w.Code)
+	}
+}
+
+func TestAuthToken_NotConfigured(t *testing.T) {
+	h := newTestHandler("", "", "", &stubAuthClient{})
+
+	body := `{"username":"rock","password":"pass"}`
+	r := httptest.NewRequest("POST", "/auth/token", strings.NewReader(body))
+	w := httptest.NewRecorder()
+
+	h.handleAuthToken(w, r)
+
+	if w.Code != 503 {
+		t.Errorf("expected 503, got %d", w.Code)
+	}
+}
+
+func TestAuthToken_UpstreamError(t *testing.T) {
+	stub := &stubAuthClient{err: io.ErrUnexpectedEOF}
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", stub)
+
+	body := `{"username":"rock","password":"pass"}`
+	r := httptest.NewRequest("POST", "/auth/token", strings.NewReader(body))
+	w := httptest.NewRecorder()
+
+	h.handleAuthToken(w, r)
+
+	if w.Code != 502 {
+		t.Errorf("expected 502, got %d", w.Code)
+	}
+}
+
+func TestAuthToken_UpstreamRejectsCredentials(t *testing.T) {
+	stub := &stubAuthClient{
+		statusCode: 400,
+		body:       `{"error":"invalid_grant","error_description":"bad password"}`,
+	}
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", stub)
+
+	body := `{"username":"rock","password":"wrong"}`
+	r := httptest.NewRequest("POST", "/auth/token", strings.NewReader(body))
+	w := httptest.NewRecorder()
+
+	h.handleAuthToken(w, r)
+
+	// Upstream error forwarded verbatim
+	if w.Code != 400 {
+		t.Errorf("expected 400 (forwarded), got %d", w.Code)
+	}
+	if !strings.Contains(w.Body.String(), "invalid_grant") {
+		t.Errorf("expected upstream error forwarded, got %s", w.Body.String())
+	}
+}
+
+// --- /auth/refresh tests ---
+
+func TestAuthRefresh_Success(t *testing.T) {
+	stub := &stubAuthClient{
+		statusCode: 200,
+		body:       `{"access_token":"new.jwt","refresh_token":"new.refresh","expires_in":3600}`,
+	}
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", stub)
+
+	body := `{"refresh_token":"old.refresh"}`
+	r := httptest.NewRequest("POST", "/auth/refresh", strings.NewReader(body))
+	w := httptest.NewRecorder()
+
+	h.handleAuthRefresh(w, r)
+
+	if w.Code != 200 {
+		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+	if stub.lastForm.Get("grant_type") != "refresh_token" {
+		t.Errorf("grant_type = %q, want refresh_token", stub.lastForm.Get("grant_type"))
+	}
+	if stub.lastForm.Get("refresh_token") != "old.refresh" {
+		t.Errorf("refresh_token not sent")
+	}
+}
+
+func TestAuthRefresh_MissingToken(t *testing.T) {
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", &stubAuthClient{})
+
+	r := httptest.NewRequest("POST", "/auth/refresh", strings.NewReader(`{}`))
+	w := httptest.NewRecorder()
+
+	h.handleAuthRefresh(w, r)
+
+	if w.Code != 400 {
+		t.Errorf("expected 400, got %d", w.Code)
+	}
+}
+
+func TestAuthRefresh_WrongMethod(t *testing.T) {
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", &stubAuthClient{})
+
+	r := httptest.NewRequest("GET", "/auth/refresh", nil)
+	w := httptest.NewRecorder()
+
+	h.handleAuthRefresh(w, r)
+
+	if w.Code != 405 {
+		t.Errorf("expected 405, got %d", w.Code)
+	}
+}
+
+func TestAuthRefresh_NotConfigured(t *testing.T) {
+	h := newTestHandler("", "", "", &stubAuthClient{})
+
+	r := httptest.NewRequest("POST", "/auth/refresh", strings.NewReader(`{"refresh_token":"x"}`))
+	w := httptest.NewRecorder()
+
+	h.handleAuthRefresh(w, r)
+
+	if w.Code != 503 {
+		t.Errorf("expected 503, got %d", w.Code)
+	}
+}
+
+func TestAuthRefresh_ExpiredToken(t *testing.T) {
+	stub := &stubAuthClient{
+		statusCode: 401,
+		body:       `{"error":"invalid_grant","error_description":"token expired"}`,
+	}
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", stub)
+
+	r := httptest.NewRequest("POST", "/auth/refresh", strings.NewReader(`{"refresh_token":"expired"}`))
+	w := httptest.NewRecorder()
+
+	h.handleAuthRefresh(w, r)
+
+	if w.Code != 401 {
+		t.Errorf("expected 401 (forwarded), got %d", w.Code)
+	}
+}
+
+// Verify no credentials are leaked in response bodies
+func TestAuthToken_NoCredentialLeak(t *testing.T) {
+	stub := &stubAuthClient{statusCode: 200, body: `{"access_token":"tok"}`}
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "super-secret", stub)
+
+	body := `{"username":"rock","password":"my-password"}`
+	r := httptest.NewRequest("POST", "/auth/token", bytes.NewReader([]byte(body)))
+	w := httptest.NewRecorder()
+
+	h.handleAuthToken(w, r)
+
+	respBody := w.Body.String()
+	if strings.Contains(respBody, "super-secret") {
+		t.Error("client_secret leaked in response")
+	}
+	if strings.Contains(respBody, "my-password") {
+		t.Error("password leaked in response")
+	}
+}

internal/proxy/proxy.go

@@ -29,6 +29,8 @@ type Handler struct {
 	config *config.Config
 	// jwtValidator validates JWT tokens for authenticated endpoints
 	jwtValidator *auth.Validator
+	// authHTTP is the HTTP client for token exchange with the identity provider.
+	authHTTP authClient
 	// Default timeouts for synthesized routes (model-based dispatch)
 	defaultConnectTimeout time.Duration
 	defaultReadTimeout    time.Duration
@@ -86,6 +88,10 @@ func New(cfg *config.Config) *Handler {
 		)
 	}
 
+	if cfg.Auth.TokenURL != "" {
+		h.authHTTP = newAuthClient()
+	}
+
 	for name, route := range cfg.Routes {
 		// Create a transport per unique upstream address for connection reuse
 		transport := h.getOrCreateTransport(route.Upstream.Address, &route.Upstream)
@@ -228,6 +234,16 @@ func writeProblemDetail(w http.ResponseWriter, status int, problemType, title, d
 
 // ServeHTTP implements http.Handler.
 func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// Auth endpoints — no JWT required (they issue tokens)
+	if r.URL.Path == "/auth/token" {
+		h.handleAuthToken(w, r)
+		return
+	}
+	if r.URL.Path == "/auth/refresh" {
+		h.handleAuthRefresh(w, r)
+		return
+	}
+
 	// Handle /v1/models endpoint (no routing needed, derived from config)
 	if r.URL.Path == "/v1/models" && r.Method == "GET" {
 		h.handleModelsEndpoint(w, r)