Give ingest a real tenant identity (write-routing deferred, disclosed)

Ingest tenant-awareness was named "undesigned, not just unbuilt" across
CLAUDE.md/threat-model.md/the runbook since early Phase 4 -- the last
major standing gap. Scoping was agreed via AskUserQuestion: a
config-supplied tenant_id + shared-secret token ingest validates
(smaller real implementation, no new PKI), over per-tenant mTLS
certs. This change builds that identity mechanism end to end and
attaches it to every record at the point it enters the system; it
deliberately does NOT build per-tenant write-routing for ClickHouse or
Tantivy -- that's real, separately-scoped follow-up work, disclosed
explicitly everywhere this was previously called undesigned, not
silently left half-done.

New pieces:

- metadata/migrations/0034 + enterprise/internal/rbacstore/
  ingest_credentials.go: a per-tenant bearer credential, only its
  SHA-256 hash ever persisted (same reasoning a password gets hashed,
  not stored raw) -- CreateIngestCredential returns the plaintext
  exactly once, ValidateIngestCredential/RevokeIngestCredential/
  ListIngestCredentialsForTenant round it out.
- enterprise-auth gains -create-ingest-credential-tenant/
  -list-ingest-credentials-tenant/-revoke-ingest-credential (same
  offline-operator-flag shape as every other credential-minting flag in
  this binary) and a new POST /internal/authorize-ingest endpoint
  (internal/authhandler) validating a presented token and resolving its
  tenant -- a genuinely different credential type from session-backed
  /internal/authorize, so it doesn't touch session.Manager at all.
- ingest (AGPL core) gains an optional TenantResolver
  (internal/grpcserver, nil by default) and its HTTP client
  implementation (internal/tenantresolver.HTTPResolver) -- a plain HTTP
  call to enterprise-auth's new endpoint, never an enterprise/ import,
  same "network boundary, not import boundary" shape
  api/authz.HTTPAuthorizer already uses for the query path.
  PushBatch now requires an `authorization: Bearer <token>` gRPC
  metadata entry once a resolver is configured, fails the whole batch
  closed on a missing/invalid credential (never falls back to "no
  tenant"), and attaches the resolved tenant ID to every record as a
  `tenant_id` Kafka message header before producing it.

Verified with real round trips at every layer, no Docker needed:
rbacstore's credential CRUD (skip-gated on live Postgres, same as every
other rbacstore integration test this phase), authhandler's new
endpoint (real HTTP via httptest, including the regression test that a
session token must not validate as an ingest credential), tenantresolver
(real HTTP client against httptest, same pattern as
authz.HTTPAuthorizer's own tests), and grpcserver's PushBatch (fake
resolver/producer -- no resolver leaves messages unchanged, a configured
resolver attaches the right header or fails closed on a bad/missing
token).

Helm: ingest.requireTenantCredential (default false) is a deliberate,
separate opt-in from enterprise.enabled -- turning ENTERPRISE_AUTH_URL
on for ingest requires every agent to already hold a credential or be
refused outright, so it must not default on just because
enterprise.enabled does (same reasoning api.yaml's ENTERPRISE_AUTH_URL
isn't tied to enterprise.enabled directly either). docker-compose.yml
leaves it unset, same as ever.

Docs updated everywhere this was called "undesigned": CLAUDE.md,
docs/architecture.md, docs/security/threat-model.md (including its
summary table, now split into "identity: built" vs "write-routing: not
yet"), docs/phase-4-runbook.md (new §13), enterprise/README.md.

ingest/internal/grpcserver/server_test.go

@@ -2,12 +2,16 @@ package grpcserver
 
 import (
 	"context"
+	"errors"
 	"io"
 	"log/slog"
 	"sync"
 	"testing"
 
 	"github.com/segmentio/kafka-go"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/status"
 	"google.golang.org/protobuf/proto"
 
 	"github.com/sentry/sentry/ingest/internal/config"
@@ -32,8 +36,35 @@ func (f *fakeProducer) WriteBatch(_ context.Context, msgs []kafka.Message) error
 	return nil
 }
 
+// fakeResolver is an in-memory stand-in for
+// ingest/internal/tenantresolver.HTTPResolver, keyed by token.
+type fakeResolver struct {
+	tenantByToken map[string]string
+}
+
+func (f *fakeResolver) ResolveTenant(_ context.Context, token string) (string, error) {
+	tenantID, ok := f.tenantByToken[token]
+	if !ok {
+		return "", errors.New("fakeResolver: unknown token")
+	}
+	return tenantID, nil
+}
+
 func newTestServer(p batchProducer) *Server {
-	return New(slog.New(slog.NewTextHandler(io.Discard, nil)), config.GRPCConfig{}, config.TLSConfig{}, p)
+	return New(slog.New(slog.NewTextHandler(io.Discard, nil)), config.GRPCConfig{}, config.TLSConfig{}, p, nil)
+}
+
+func newTestServerWithResolver(p batchProducer, resolver TenantResolver) *Server {
+	return New(slog.New(slog.NewTextHandler(io.Discard, nil)), config.GRPCConfig{}, config.TLSConfig{}, p, resolver)
+}
+
+// contextWithBearerToken builds an incoming gRPC context carrying an
+// "authorization: Bearer <token>" metadata entry -- the shape a real
+// grpc-go server hands PushBatch once TLS/framing is stripped away, so
+// this exercises the same metadata.FromIncomingContext path production
+// traffic does, not a shortcut around it.
+func contextWithBearerToken(token string) context.Context {
+	return metadata.NewIncomingContext(context.Background(), metadata.Pairs("authorization", "Bearer "+token))
 }
 
 func TestPushBatchAssignsRecordID(t *testing.T) {
@@ -124,3 +155,101 @@ func TestPushBatchEmptyRecordsIsANoOp(t *testing.T) {
 		t.Fatalf("expected no batches written for an empty request, got %d", len(fp.written))
 	}
 }
+
+// TestPushBatchNoResolverAttachesNoTenantHeader is the regression test
+// for single-tenant deployments' behavior staying unchanged: with no
+// TenantResolver configured, records are produced exactly as before --
+// no tenant_id header at all -- even with a bearer token present (it's
+// simply never inspected).
+func TestPushBatchNoResolverAttachesNoTenantHeader(t *testing.T) {
+	fp := &fakeProducer{}
+	s := newTestServer(fp)
+
+	req := &logsv1.PushBatchRequest{Records: []*logsv1.LogRecord{{Host: "h1", Message: "one"}}}
+	if _, err := s.PushBatch(contextWithBearerToken("irrelevant"), req); err != nil {
+		t.Fatalf("PushBatch() error = %v", err)
+	}
+
+	fp.mu.Lock()
+	defer fp.mu.Unlock()
+	for _, h := range fp.written[0][0].Headers {
+		if h.Key == TenantIDHeaderKey {
+			t.Fatalf("expected no %s header with no resolver configured, got %q", TenantIDHeaderKey, h.Value)
+		}
+	}
+}
+
+func TestPushBatchWithResolverAttachesTenantHeader(t *testing.T) {
+	fp := &fakeProducer{}
+	resolver := &fakeResolver{tenantByToken: map[string]string{"real-token": "acme"}}
+	s := newTestServerWithResolver(fp, resolver)
+
+	req := &logsv1.PushBatchRequest{Records: []*logsv1.LogRecord{
+		{Host: "h1", Message: "one"},
+		{Host: "h1", Message: "two"},
+	}}
+	if _, err := s.PushBatch(contextWithBearerToken("real-token"), req); err != nil {
+		t.Fatalf("PushBatch() error = %v", err)
+	}
+
+	fp.mu.Lock()
+	defer fp.mu.Unlock()
+	if len(fp.written[0]) != 2 {
+		t.Fatalf("expected 2 messages written, got %d", len(fp.written[0]))
+	}
+	for _, msg := range fp.written[0] {
+		found := false
+		for _, h := range msg.Headers {
+			if h.Key == TenantIDHeaderKey {
+				found = true
+				if string(h.Value) != "acme" {
+					t.Fatalf("%s header = %q, want acme", TenantIDHeaderKey, h.Value)
+				}
+			}
+		}
+		if !found {
+			t.Fatalf("expected every record to carry a %s header", TenantIDHeaderKey)
+		}
+	}
+}
+
+func TestPushBatchWithResolverRejectsMissingToken(t *testing.T) {
+	fp := &fakeProducer{}
+	resolver := &fakeResolver{tenantByToken: map[string]string{"real-token": "acme"}}
+	s := newTestServerWithResolver(fp, resolver)
+
+	req := &logsv1.PushBatchRequest{Records: []*logsv1.LogRecord{{Host: "h1", Message: "one"}}}
+	_, err := s.PushBatch(context.Background(), req) // no bearer token in context at all
+	if status.Code(err) != codes.Unauthenticated {
+		t.Fatalf("PushBatch() error = %v, want Unauthenticated", err)
+	}
+
+	fp.mu.Lock()
+	defer fp.mu.Unlock()
+	if len(fp.written) != 0 {
+		t.Fatal("a batch with no bearer token must never reach the producer once a resolver is configured")
+	}
+}
+
+// TestPushBatchWithResolverRejectsInvalidToken is the fail-closed
+// regression test: a resolver configured but a token it doesn't
+// recognize must refuse the whole batch, never fall back to "no tenant"
+// (which would silently defeat the point of requiring a credential at
+// all).
+func TestPushBatchWithResolverRejectsInvalidToken(t *testing.T) {
+	fp := &fakeProducer{}
+	resolver := &fakeResolver{tenantByToken: map[string]string{"real-token": "acme"}}
+	s := newTestServerWithResolver(fp, resolver)
+
+	req := &logsv1.PushBatchRequest{Records: []*logsv1.LogRecord{{Host: "h1", Message: "one"}}}
+	_, err := s.PushBatch(contextWithBearerToken("wrong-token"), req)
+	if status.Code(err) != codes.Unauthenticated {
+		t.Fatalf("PushBatch() error = %v, want Unauthenticated", err)
+	}
+
+	fp.mu.Lock()
+	defer fp.mu.Unlock()
+	if len(fp.written) != 0 {
+		t.Fatal("a batch with an invalid token must never reach the producer once a resolver is configured")
+	}
+}