feat: replace static API token with per-request Gitea PAT pass-through

Callers now supply their own Gitea PAT as a Bearer token; the server validates
it against GET /api/v1/user and threads it through context to all downstream
Gitea API calls. GITEA_API_TOKEN env var and the GiteaAPIToken config field are
removed.

internal/auth/bearer.go

@@ -0,0 +1,49 @@
+package auth
+
+import (
+	"context"
+	"net/http"
+	"strings"
+	"time"
+)
+
+type tokenKey struct{}
+
+// BearerMiddleware validates the incoming bearer token as a Gitea PAT by
+// calling GET /api/v1/user. The validated token is stored in context for
+// downstream use by the Gitea client.
+func BearerMiddleware(giteaBaseURL string, next http.Handler) http.Handler {
+	hc := &http.Client{Timeout: 5 * time.Second}
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		token, ok := strings.CutPrefix(r.Header.Get("Authorization"), "Bearer ")
+		if !ok || token == "" {
+			http.Error(w, "unauthorized", http.StatusUnauthorized)
+			return
+		}
+		req, err := http.NewRequestWithContext(r.Context(), http.MethodGet, giteaBaseURL+"/api/v1/user", nil)
+		if err != nil {
+			http.Error(w, "unauthorized", http.StatusUnauthorized)
+			return
+		}
+		req.Header.Set("Authorization", "token "+token)
+		resp, err := hc.Do(req)
+		if err != nil || resp.StatusCode != http.StatusOK {
+			if resp != nil {
+				_ = resp.Body.Close()
+			}
+			http.Error(w, "unauthorized", http.StatusUnauthorized)
+			return
+		}
+		_ = resp.Body.Close()
+		ctx := context.WithValue(r.Context(), tokenKey{}, token)
+		next.ServeHTTP(w, r.WithContext(ctx))
+	})
+}
+
+// TokenFromContext returns the validated Gitea PAT stored by BearerMiddleware.
+func TokenFromContext(ctx context.Context) string {
+	if v, ok := ctx.Value(tokenKey{}).(string); ok {
+		return v
+	}
+	return ""
+}

internal/auth/bearer_test.go

@@ -0,0 +1,82 @@
+package auth_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"gitea.d-ma.be/mathias/gitea-mcp/internal/auth"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestBearerMiddleware_NoAuthHeader(t *testing.T) {
+	srv := httptest.NewServer(auth.BearerMiddleware("https://gitea.example.com",
+		http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+			w.WriteHeader(http.StatusOK)
+		}),
+	))
+	defer srv.Close()
+
+	resp, err := http.Post(srv.URL+"/mcp", "application/json", nil)
+	require.NoError(t, err)
+	defer resp.Body.Close()
+	assert.Equal(t, http.StatusUnauthorized, resp.StatusCode)
+}
+
+func TestBearerMiddleware_InvalidToken(t *testing.T) {
+	// Mock Gitea that rejects the token
+	giteaMock := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusUnauthorized)
+	}))
+	defer giteaMock.Close()
+
+	srv := httptest.NewServer(auth.BearerMiddleware(giteaMock.URL,
+		http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+			w.WriteHeader(http.StatusOK)
+		}),
+	))
+	defer srv.Close()
+
+	req, _ := http.NewRequest(http.MethodPost, srv.URL+"/mcp", nil)
+	req.Header.Set("Authorization", "Bearer bad-token")
+	resp, err := http.DefaultClient.Do(req)
+	require.NoError(t, err)
+	defer resp.Body.Close()
+	assert.Equal(t, http.StatusUnauthorized, resp.StatusCode)
+}
+
+func TestBearerMiddleware_ValidToken(t *testing.T) {
+	const token = "valid-pat"
+
+	// Mock Gitea that accepts the token and returns a user
+	giteaMock := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assert.Equal(t, "token "+token, r.Header.Get("Authorization"))
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer giteaMock.Close()
+
+	called := false
+	srv := httptest.NewServer(auth.BearerMiddleware(giteaMock.URL,
+		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			called = true
+			// Token must be available in context for downstream Gitea client
+			assert.Equal(t, token, auth.TokenFromContext(r.Context()))
+			w.WriteHeader(http.StatusOK)
+		}),
+	))
+	defer srv.Close()
+
+	req, _ := http.NewRequest(http.MethodPost, srv.URL+"/mcp", nil)
+	req.Header.Set("Authorization", "Bearer "+token)
+	resp, err := http.DefaultClient.Do(req)
+	require.NoError(t, err)
+	defer resp.Body.Close()
+	assert.Equal(t, http.StatusOK, resp.StatusCode)
+	assert.True(t, called)
+}
+
+func TestTokenFromContext_Empty(t *testing.T) {
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	assert.Equal(t, "", auth.TokenFromContext(req.Context()))
+}