feat(proxy): add /auth/exchange token exchange endpoint

Closes homelab#10 (P3.5) ## Endpoint `POST /auth/exchange` — RFC 8693-inspired token exchange. ## Flow 1. Validate `subject_token` (user JWT) via gateway's JWKS validator 2. Authenticate service via `client_credentials` against Authentik 3. Verify requested `scope` is subset of service's roles (deny escalation) 4. Return service token + subject identity metadata ## Request ```json {"subject_token": "<user JWT>", "client_id": "portfolio-agent", "client_secret": "<secret>", "scope": "memory:read", "resource": "poimen-memory"} ``` ## Response ```json {"access_token": "<service JWT>", "subject": "user-hash", "acting_party": "portfolio-agent", "scope": "memory:read"} ```
2026-09-09 00:31:10 +00:00
parent a51c14426f
commit 359645f397
3 changed files with 448 additions and 0 deletions
@@ -0,0 +1,215 @@
+package proxy
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"forgejo.riotpiao.com/rock/homelab-frontend/internal/auth"
+	"forgejo.riotpiao.com/rock/homelab-frontend/internal/config"
+)
+
+// fakeJWT creates a JWT-shaped string (header.payload.signature) with given claims.
+// Not cryptographically signed — used only with stubbed validators.
+func fakeJWT(claims map[string]interface{}) string {
+	header := base64.RawURLEncoding.EncodeToString([]byte(`{"alg":"none","typ":"JWT"}`))
+	payload, _ := json.Marshal(claims)
+	payloadB64 := base64.RawURLEncoding.EncodeToString(payload)
+	return header + "." + payloadB64 + ".fakesig"
+}
+
+// stubJWTValidator returns claims from a pre-set map keyed by token.
+type stubJWTValidator struct {
+	tokens map[string]map[string]interface{}
+}
+
+func (s *stubJWTValidator) ValidateBearerToken(authHeader string) (map[string]interface{}, error) {
+	token := strings.TrimPrefix(authHeader, "Bearer ")
+	if claims, ok := s.tokens[token]; ok {
+		return claims, nil
+	}
+	return nil, fmt.Errorf("invalid token")
+}
+
+func (s *stubJWTValidator) CheckPermissions(claims map[string]interface{}, required ...string) bool {
+	return true
+}
+
+// We can't use stubJWTValidator directly because Handler expects *auth.Validator.
+// Instead, test via the endpoint with a real JWKS server or test the helpers directly.
+
+func TestScopeSubset(t *testing.T) {
+	tests := []struct {
+		requested string
+		allowed   []string
+		want      bool
+	}{
+		{"memory:read", []string{"llm:inference", "memory:read"}, true},
+		{"memory:read memory:write", []string{"memory:read", "memory:write"}, true},
+		{"memory:write", []string{"memory:read"}, false},
+		{"admin:*", []string{"memory:read"}, false},
+		{"anything", []string{"*"}, true},
+		{"", []string{"memory:read"}, true},
+		{"memory:read", []string{}, false},
+	}
+	for _, tt := range tests {
+		got := scopeSubset(tt.requested, tt.allowed)
+		if got != tt.want {
+			t.Errorf("scopeSubset(%q, %v) = %v, want %v", tt.requested, tt.allowed, got, tt.want)
+		}
+	}
+}
+
+func TestExtractRolesFromJWT(t *testing.T) {
+	token := fakeJWT(map[string]interface{}{
+		"roles": []interface{}{"llm:inference", "memory:read"},
+		"sub":   "test-user",
+	})
+
+	roles, err := extractRolesFromJWT(token)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(roles) != 2 || roles[0] != "llm:inference" || roles[1] != "memory:read" {
+		t.Errorf("roles = %v, want [llm:inference memory:read]", roles)
+	}
+}
+
+func TestExtractRolesFromJWT_InvalidFormat(t *testing.T) {
+	_, err := extractRolesFromJWT("not-a-jwt")
+	if err == nil {
+		t.Error("expected error for invalid JWT")
+	}
+}
+
+func TestExtractRolesFromJWT_NoRoles(t *testing.T) {
+	token := fakeJWT(map[string]interface{}{"sub": "user"})
+	roles, err := extractRolesFromJWT(token)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if roles != nil {
+		t.Errorf("expected nil roles, got %v", roles)
+	}
+}
+
+func TestHandleAuthExchange_WrongMethod(t *testing.T) {
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", &stubAuthClient{})
+	h.jwtValidator = auth.NewValidator("", "", "")
+
+	r := httptest.NewRequest("GET", "/auth/exchange", nil)
+	w := httptest.NewRecorder()
+
+	h.handleAuthExchange(w, r)
+
+	if w.Code != 405 {
+		t.Errorf("expected 405, got %d", w.Code)
+	}
+}
+
+func TestHandleAuthExchange_NotConfigured(t *testing.T) {
+	h := &Handler{
+		config: &config.Config{},
+		routes: make(map[string]*Route),
+		transports: make(map[string]*http.Transport),
+	}
+
+	body := `{"subject_token":"x","client_id":"y","client_secret":"z"}`
+	r := httptest.NewRequest("POST", "/auth/exchange", strings.NewReader(body))
+	w := httptest.NewRecorder()
+
+	h.handleAuthExchange(w, r)
+
+	if w.Code != 503 {
+		t.Errorf("expected 503, got %d", w.Code)
+	}
+}
+
+func TestHandleAuthExchange_MissingFields(t *testing.T) {
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", &stubAuthClient{})
+	h.jwtValidator = auth.NewValidator("", "", "")
+
+	tests := []struct {
+		name string
+		body string
+	}{
+		{"missing subject", `{"client_id":"x","client_secret":"y"}`},
+		{"missing client_id", `{"subject_token":"x","client_secret":"y"}`},
+		{"missing client_secret", `{"subject_token":"x","client_id":"y"}`},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			r := httptest.NewRequest("POST", "/auth/exchange", strings.NewReader(tt.body))
+			w := httptest.NewRecorder()
+			h.handleAuthExchange(w, r)
+			if w.Code != 400 {
+				t.Errorf("expected 400, got %d", w.Code)
+			}
+		})
+	}
+}
+
+func TestHandleAuthExchange_InvalidJSON(t *testing.T) {
+	h := newTestHandler("https://auth.example.com/token/", "api-gw", "secret", &stubAuthClient{})
+	h.jwtValidator = auth.NewValidator("", "", "")
+
+	r := httptest.NewRequest("POST", "/auth/exchange", strings.NewReader("not json"))
+	w := httptest.NewRecorder()
+
+	h.handleAuthExchange(w, r)
+
+	if w.Code != 400 {
+		t.Errorf("expected 400, got %d", w.Code)
+	}
+}
+
+func TestHandleAuthExchange_ScopeEscalation(t *testing.T) {
+	// Test scopeSubset directly since full integration needs JWKS
+	if scopeSubset("admin:delete", []string{"memory:read", "memory:write"}) {
+		t.Error("scope escalation should be denied")
+	}
+	if !scopeSubset("memory:read", []string{"memory:read", "memory:write"}) {
+		t.Error("valid scope should be allowed")
+	}
+}
+
+func TestClaimStr(t *testing.T) {
+	claims := map[string]interface{}{"sub": "user-1", "num": 42, "nil": nil}
+	if got := claimStr(claims, "sub"); got != "user-1" {
+		t.Errorf("claimStr(sub) = %q, want user-1", got)
+	}
+	if got := claimStr(claims, "num"); got != "" {
+		t.Errorf("claimStr(num) = %q, want empty", got)
+	}
+	if got := claimStr(claims, "nil"); got != "" {
+		t.Errorf("claimStr(nil) = %q, want empty", got)
+	}
+	if got := claimStr(claims, "missing"); got != "" {
+		t.Errorf("claimStr(missing) = %q, want empty", got)
+	}
+}
+
+func TestClaimStrSlice(t *testing.T) {
+	claims := map[string]interface{}{
+		"roles": []interface{}{"a", "b", "", nil, 42},
+		"empty": []interface{}{},
+		"str":   "not-a-slice",
+	}
+	if got := claimStrSlice(claims, "roles"); len(got) != 2 || got[0] != "a" || got[1] != "b" {
+		t.Errorf("claimStrSlice(roles) = %v, want [a b]", got)
+	}
+	if got := claimStrSlice(claims, "empty"); len(got) != 0 {
+		t.Errorf("claimStrSlice(empty) = %v, want empty", got)
+	}
+	if got := claimStrSlice(claims, "str"); got != nil {
+		t.Errorf("claimStrSlice(str) = %v, want nil", got)
+	}
+	if got := claimStrSlice(claims, "missing"); got != nil {
+		t.Errorf("claimStrSlice(missing) = %v, want nil", got)
+	}
+}