feat(nano): federating hasJoined multiplexer with per-source UUID namespacing

internal/api/api.go

@@ -115,6 +115,13 @@ type API struct {
 	// positive value. Enforced via streamGate in the two relay handlers.
 	MaxStreamsPerPrincipal int
 
+	// AuthSources is the Felis-nano multi-source hasJoined multiplexer's upstream
+	// Yggdrasil list, in priority order (config order; the Mojang Identity source
+	// first for 正版优先). Nil — the default — makes the session verifier reject every
+	// login (204), so the endpoint ships inert until cmd/felis wires configured
+	// sources. Consumed by handleHasJoined (handlers_hasjoined.go).
+	AuthSources []AuthSource
+
 	// Now is the clock, injectable for tests. Defaults to time.Now.
 	Now func() time.Time
 
@@ -260,6 +267,13 @@ func (a *API) internalAPIRoutes() []apiRoute {
 		// Mojang player (same name, different UUID) always passes.
 		{Method: "POST", Pattern: "/api/v1/internal/player/reclaim", h: a.handleReclaimUsername},
 		{Method: "GET", Pattern: "/api/v1/internal/player/blacklist/{mc_uuid}", h: a.handleCheckBlacklist},
+		// Felis-nano multi-source session verifier (spec §B3 player game-login).
+		// Velocity's authlib is pointed here (-Dmojang.sessionserver or a thin login
+		// hook); it speaks the vanilla sessionserver protocol and carries no token, so
+		// this is Public. It fans hasJoined out to the configured Yggdrasil roots
+		// (Mojang-first) and rewrites third-party UUIDs into a per-source namespace
+		// before returning the canonical profile (handlers_hasjoined.go).
+		{Method: "GET", Pattern: "/session/minecraft/hasJoined", Public: true, h: a.handleHasJoined},
 		// Op-login (passwordless console login): an in-game op requests a login that
 		// the web owner/admin approves, then redeems for a session. Internal face
 		// carries the pending queue and the approve action (service-token auth, no

internal/api/handlers_hasjoined.go

@@ -0,0 +1,143 @@
+package api
+
+import (
+	"context"
+	"encoding/hex"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/url"
+	"time"
+
+	"github.com/google/uuid"
+)
+
+// Felis-nano: the multi-source hasJoined multiplexer (spec §B3 player game-login).
+//
+// Velocity's session verifier (authlib) is pointed here — via -Dmojang.sessionserver
+// on Felis-managed proxies, or a thin login-pipeline hook on third-party servers. On
+// login Velocity computes the serverId hash and GETs hasJoined; this endpoint fans that
+// query out to the configured Yggdrasil roots in priority order (Mojang first, 正版优先)
+// and returns the first source that validates. Each upstream Yggdrasil runs its own
+// serverId-hash check — the multiplexer only relays, it computes no hashes.
+//
+// The one non-negotiable transform: a non-identity (third-party) source's UUID is
+// self-asserted, so its profile is rewritten into a per-source namespace
+// (canonical = UUIDv3(felisAuthNS, tag+":"+nativeID)) BEFORE it leaves the resolver.
+// Mojang stays identity. This makes the reclaim invariant — "the genuine Mojang player
+// has a DIFFERENT UUID from any squatter" — true by construction, not assumed: MD5
+// preimage resistance means no third-party source can mint a Mojang-space UUID, and the
+// per-tag namespace means two sources cannot collide onto one identity. Every downstream
+// key (account_links, username_blacklist, owner checks) then sees one canonical UUID.
+
+// felisAuthNS is the fixed UUIDv3 namespace every third-party profile is rewritten
+// under (see the rewrite rationale above). Derived from the project name, not a magic
+// literal, so its origin is self-documenting; the exact value only has to be stable.
+var felisAuthNS = uuid.NewSHA1(uuid.NameSpaceURL, []byte("nano.felis.lolicon.best/auth-source"))
+
+// authHTTPClient calls the upstream Yggdrasil roots. The timeout bounds one login
+// against a hung source; the resolver moves on to the next source on any failure.
+// ponytail: one shared client, sequential priority scan — a third-party login costs one
+// wasted Mojang round-trip; add parallel fan-out only if login latency bites.
+var authHTTPClient = &http.Client{Timeout: 5 * time.Second}
+
+// AuthSource is one upstream Yggdrasil root in the multiplexer's priority list (config
+// order = priority). URL is the full hasJoined endpoint the query string is appended to.
+// Identity marks the authoritative source (Mojang) whose UUIDs are trusted as-is; every
+// other source is rewritten into felisAuthNS.
+type AuthSource struct {
+	Tag      string
+	URL      string
+	Identity bool
+}
+
+// sessionProfile is the Mojang hasJoined contract. properties is relayed verbatim
+// (json.RawMessage) so a source's signed textures survive the multiplexer untouched.
+type sessionProfile struct {
+	ID         string            `json:"id"`
+	Name       string            `json:"name"`
+	Properties []json.RawMessage `json:"properties,omitempty"`
+}
+
+// handleHasJoined is the multi-source session verifier (Felis-nano). It is a Public
+// internal-face route: authlib speaks the vanilla sessionserver protocol and sends no
+// service token. A rejected login is 204 No Content — exactly what Mojang returns for an
+// invalid session, which authlib maps to "failed to verify username".
+func (a *API) handleHasJoined(w http.ResponseWriter, r *http.Request) {
+	q := r.URL.Query()
+	username, serverID := q.Get("username"), q.Get("serverId")
+	if username == "" || serverID == "" {
+		w.WriteHeader(http.StatusNoContent)
+		return
+	}
+
+	prof, src := a.resolveHasJoined(r.Context(), username, serverID, q.Get("ip"))
+	if prof == nil {
+		w.WriteHeader(http.StatusNoContent)
+		return
+	}
+
+	// Canonicalize identity. A trusted (Mojang) source keeps its UUID; a self-asserted
+	// source is rewritten into felisAuthNS so it can never land in Mojang's UUID space
+	// nor onto another source's. An unparseable identity UUID is not trustworthy → reject.
+	var canonical uuid.UUID
+	if src.Identity {
+		id, err := uuid.Parse(prof.ID)
+		if err != nil {
+			w.WriteHeader(http.StatusNoContent)
+			return
+		}
+		canonical = id
+	} else {
+		canonical = uuid.NewMD5(felisAuthNS, []byte(src.Tag+":"+prof.ID))
+	}
+
+	// Bar gate at the single chokepoint every login crosses, so a reclaimed squatter
+	// stays out even on a consumer with no limbo plugin. Keyed on the dashed canonical
+	// UUID — the same form Repo.ReclaimUsername stores.
+	barred, err := a.Repo.IsUsernameBlacklisted(r.Context(), canonical.String())
+	if err != nil {
+		writeError(w, r, err)
+		return
+	}
+	if barred {
+		w.WriteHeader(http.StatusNoContent)
+		return
+	}
+
+	// Emit the canonical UUID undashed — the 32-hex form authlib's GameProfile expects.
+	prof.ID = hex.EncodeToString(canonical[:])
+	writeJSON(w, http.StatusOK, prof)
+}
+
+// resolveHasJoined queries each configured source in priority order and returns the
+// first that validates the session (200 with a profile). A source that is down, answers
+// non-200 (204 = "not my player"), or returns garbage is skipped.
+func (a *API) resolveHasJoined(ctx context.Context, username, serverID, ip string) (*sessionProfile, AuthSource) {
+	for _, src := range a.AuthSources {
+		u := src.URL + "?username=" + url.QueryEscape(username) + "&serverId=" + url.QueryEscape(serverID)
+		if ip != "" {
+			u += "&ip=" + url.QueryEscape(ip)
+		}
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
+		if err != nil {
+			continue
+		}
+		resp, err := authHTTPClient.Do(req)
+		if err != nil {
+			continue
+		}
+		if resp.StatusCode != http.StatusOK {
+			resp.Body.Close()
+			continue
+		}
+		var prof sessionProfile
+		err = json.NewDecoder(io.LimitReader(resp.Body, 1<<16)).Decode(&prof)
+		resp.Body.Close()
+		if err != nil || prof.ID == "" {
+			continue
+		}
+		return &prof, src
+	}
+	return nil, AuthSource{}
+}

internal/api/handlers_hasjoined_test.go

@@ -0,0 +1,169 @@
+package api
+
+import (
+	"encoding/hex"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/google/uuid"
+)
+
+// fakeYgg stands in for one upstream Yggdrasil root. It answers hasJoined with the
+// given profile, or 204 when id == "" ("not my player") or a query field is missing —
+// the same contract Mojang's real sessionserver honors.
+func fakeYgg(t *testing.T, id, name string) *httptest.Server {
+	t.Helper()
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		q := r.URL.Query()
+		if id == "" || q.Get("username") == "" || q.Get("serverId") == "" {
+			w.WriteHeader(http.StatusNoContent)
+			return
+		}
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"id": id, "name": name,
+			"properties": []map[string]string{{"name": "textures", "value": "SKIN", "signature": "SIG"}},
+		})
+	}))
+	t.Cleanup(srv.Close)
+	return srv
+}
+
+func getHasJoined(h http.Handler, username, serverID string) *httptest.ResponseRecorder {
+	return do(h, "GET", "/session/minecraft/hasJoined?username="+username+"&serverId="+serverID, "", nil)
+}
+
+func profileOf(t *testing.T, w *httptest.ResponseRecorder) sessionProfile {
+	t.Helper()
+	var p sessionProfile
+	if err := json.Unmarshal(w.Body.Bytes(), &p); err != nil {
+		t.Fatalf("profile body not JSON: %v (%q)", err, w.Body.String())
+	}
+	return p
+}
+
+// undashed is the 32-hex form the resolver must emit (authlib's GameProfile format).
+func undashed(u uuid.UUID) string { return hex.EncodeToString(u[:]) }
+
+const notchMojangID = "069a79f444e94726a5befca90e38aaf5" // a real Mojang-space UUID, undashed
+
+func TestHasJoined(t *testing.T) {
+	// A trusted (Mojang) source passes its UUID through byte-for-byte.
+	t.Run("mojang identity passthrough", func(t *testing.T) {
+		mojang := fakeYgg(t, notchMojangID, "Notch")
+		api := newTestAPI(newFakeRepo(), newFakeCluster())
+		api.AuthSources = []AuthSource{{Tag: "mojang", URL: mojang.URL, Identity: true}}
+
+		w := getHasJoined(api.InternalHandler(), "Notch", "abc")
+		if w.Code != http.StatusOK {
+			t.Fatalf("code = %d, want 200 (%q)", w.Code, w.Body.String())
+		}
+		p := profileOf(t, w)
+		if p.ID != notchMojangID {
+			t.Fatalf("mojang id = %q, want unchanged %q", p.ID, notchMojangID)
+		}
+		if len(p.Properties) != 1 {
+			t.Fatalf("properties not relayed: %v", p.Properties)
+		}
+	})
+
+	// THE security invariant: a self-asserted source claiming a Mojang-space UUID must
+	// NOT be emitted as-is — it is rewritten into the per-source namespace. Without this,
+	// a malicious third-party could impersonate any Mojang player with full UUID fidelity
+	// and the reclaim/blacklist layer (keyed on "genuine Mojang has a different UUID")
+	// could never catch it.
+	t.Run("thirdparty UUID rewritten, never emitted as-is", func(t *testing.T) {
+		evil := fakeYgg(t, notchMojangID, "Notch") // lies: returns real Notch's Mojang UUID
+		api := newTestAPI(newFakeRepo(), newFakeCluster())
+		api.AuthSources = []AuthSource{{Tag: "littleskin", URL: evil.URL, Identity: false}}
+
+		w := getHasJoined(api.InternalHandler(), "Notch", "abc")
+		if w.Code != http.StatusOK {
+			t.Fatalf("code = %d, want 200", w.Code)
+		}
+		got := profileOf(t, w).ID
+		if got == notchMojangID {
+			t.Fatalf("SECURITY: third-party Mojang-space UUID emitted as-is (%q) — impersonation open", got)
+		}
+		want := undashed(uuid.NewMD5(felisAuthNS, []byte("littleskin:"+notchMojangID)))
+		if got != want {
+			t.Fatalf("rewrite = %q, want deterministic UUIDv3 %q", got, want)
+		}
+	})
+
+	// Mojang is priority-first: when both would validate the same name, Mojang wins.
+	t.Run("mojang priority wins over thirdparty", func(t *testing.T) {
+		mojang := fakeYgg(t, notchMojangID, "Notch")
+		third := fakeYgg(t, "aaaaaaaaaaaa4aaaaaaaaaaaaaaaaaaa", "Notch")
+		api := newTestAPI(newFakeRepo(), newFakeCluster())
+		api.AuthSources = []AuthSource{
+			{Tag: "mojang", URL: mojang.URL, Identity: true},
+			{Tag: "littleskin", URL: third.URL, Identity: false},
+		}
+		w := getHasJoined(api.InternalHandler(), "Notch", "abc")
+		if p := profileOf(t, w); p.ID != notchMojangID {
+			t.Fatalf("id = %q, want mojang %q (priority)", p.ID, notchMojangID)
+		}
+	})
+
+	// Mojang doesn't know the player (204) → fall through to the third-party source,
+	// whose profile is returned rewritten.
+	t.Run("fallthrough to thirdparty when mojang 204s", func(t *testing.T) {
+		mojang := fakeYgg(t, "", "") // 204: not my player
+		third := fakeYgg(t, notchMojangID, "Notch")
+		api := newTestAPI(newFakeRepo(), newFakeCluster())
+		api.AuthSources = []AuthSource{
+			{Tag: "mojang", URL: mojang.URL, Identity: true},
+			{Tag: "littleskin", URL: third.URL, Identity: false},
+		}
+		w := getHasJoined(api.InternalHandler(), "Notch", "abc")
+		if w.Code != http.StatusOK {
+			t.Fatalf("code = %d, want 200", w.Code)
+		}
+		want := undashed(uuid.NewMD5(felisAuthNS, []byte("littleskin:"+notchMojangID)))
+		if p := profileOf(t, w); p.ID != want {
+			t.Fatalf("id = %q, want rewritten thirdparty %q", p.ID, want)
+		}
+	})
+
+	// No source validates → 204 (authlib maps this to a verify failure).
+	t.Run("no source validates -> 204", func(t *testing.T) {
+		a := fakeYgg(t, "", "")
+		b := fakeYgg(t, "", "")
+		api := newTestAPI(newFakeRepo(), newFakeCluster())
+		api.AuthSources = []AuthSource{
+			{Tag: "mojang", URL: a.URL, Identity: true},
+			{Tag: "littleskin", URL: b.URL, Identity: false},
+		}
+		if w := getHasJoined(api.InternalHandler(), "Ghost", "abc"); w.Code != http.StatusNoContent {
+			t.Fatalf("code = %d, want 204", w.Code)
+		}
+	})
+
+	// The reused bar gate: a barred CANONICAL UUID is rejected at the resolver, so a
+	// reclaimed squatter stays out even on a consumer with no limbo plugin. Keyed on the
+	// dashed canonical (post-rewrite), the same form Repo.ReclaimUsername stores.
+	t.Run("barred canonical UUID -> 204", func(t *testing.T) {
+		third := fakeYgg(t, notchMojangID, "Notch")
+		repo := newFakeRepo()
+		canonical := uuid.NewMD5(felisAuthNS, []byte("littleskin:"+notchMojangID))
+		repo.blacklist[canonical.String()] = true // barred by a prior reclaim
+		api := newTestAPI(repo, newFakeCluster())
+		api.AuthSources = []AuthSource{{Tag: "littleskin", URL: third.URL, Identity: false}}
+
+		if w := getHasJoined(api.InternalHandler(), "Notch", "abc"); w.Code != http.StatusNoContent {
+			t.Fatalf("barred login: code = %d, want 204", w.Code)
+		}
+	})
+
+	// Missing query fields → 204 without touching any source.
+	t.Run("missing username -> 204", func(t *testing.T) {
+		api := newTestAPI(newFakeRepo(), newFakeCluster())
+		api.AuthSources = []AuthSource{{Tag: "mojang", URL: "http://127.0.0.1:0", Identity: true}}
+		w := do(api.InternalHandler(), "GET", "/session/minecraft/hasJoined?serverId=abc", "", nil)
+		if w.Code != http.StatusNoContent {
+			t.Fatalf("code = %d, want 204", w.Code)
+		}
+	})
+}