fix(oidc/prelogin): encrypt state/nonce/PKCE-verifier at rest (HIGH-5)

Pre-login rows previously persisted the OIDC state, nonce, and PKCE
verifier as plaintext columns; an operator restoring an unredacted
backup of oidc_pre_login_sessions to a debug environment leaked every
in-flight handshake. If the IdP also leaked the auth code in the same
window (logged at a misconfigured TLS terminator, etc.), the attacker
could exchange code + verifier directly. RFC 7636 §7 requires verifier
confidentiality.

This commit:
- Migration 000041 adds {state,nonce,pkce_verifier}_enc BYTEA columns
  and makes the legacy plaintext columns nullable. A follow-up
  migration drops the plaintext columns once the rolling deploy
  completes.
- internal/repository/postgres/oidc_prelogin.go::Create encrypts the
  three secrets via crypto.EncryptIfKeySet (v3 magic 0x03 + per-row
  salt + nonce + AES-256-GCM tag) and writes only the encrypted
  columns; legacy plaintext stays NULL on the write path.
- LookupAndConsume prefers encrypted columns via materialize(),
  falling back to the legacy plaintext only when _enc is NULL — the
  rolling-deploy compat layer that 000042 will retire.
- NewPreLoginRepository takes encryptionKey; cmd/server/main.go threads
  cfg.Encryption.ConfigEncryptionKey in.
- Encryption key reuses CERTCTL_CONFIG_ENCRYPTION_KEY (same passphrase
  already protecting OIDC client secrets and SessionSigningKey material).
  No new env var.

Why encryption-at-rest, not HMAC: the spec's HMAC approach required
moving plaintext into the cookie (the cookie currently carries only
row ID + HMAC). Re-shaping the cookie wire format would be a larger
refactor; the audit explicitly admits encryption-at-rest is an
acceptable closure (weaker because backups still contain decryptable
ciphertext, but the encryption key is held separately from the DB
backup, and the 10-minute TTL further bounds usable secret window).

Three new regression tests in oidc_prelogin_encryption_test.go pin:
  (a) _enc columns contain v3-format ciphertext, NOT plaintext
      substrings, post-Create
  (b) legacy plaintext columns are NULL post-Create (defends against
      future patches that re-introduce plaintext writes)
  (c) LookupAndConsume round-trips state/nonce/verifier byte-for-byte
A fourth test pins the legacy-row fallback for rolling-deploy compat.

Refs: cowork/auth-bundles-audit-2026-05-10.md HIGH-5
Spec: cowork/auth-bundles-fixes-2026-05-10/09-high-5-prelogin-secret-protection.md

cmd/server/main.go

@@ -396,7 +396,10 @@ func main() {
 	oidcProviderRepo := postgres.NewOIDCProviderRepository(db)
 	oidcMappingRepo := postgres.NewGroupRoleMappingRepository(db)
 	oidcUserRepo := postgres.NewUserRepository(db)
-	oidcPreLoginRepo := postgres.NewPreLoginRepository(db)
+	// Audit 2026-05-10 HIGH-5: thread CERTCTL_CONFIG_ENCRYPTION_KEY into the
+	// pre-login repo so state/nonce/PKCE-verifier are encrypted at rest. Same
+	// key already protects OIDC client secrets and session signing keys.
+	oidcPreLoginRepo := postgres.NewPreLoginRepository(db, cfg.Encryption.ConfigEncryptionKey)
 	preLoginAdapter := oidcsvc.NewPreLoginAdapter(
 		oidcPreLoginRepo,
 		sessionKeyRepo, // Phase 4 SessionSigningKeyRepository

internal/repository/postgres/oidc_prelogin.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"time"
 
+	cryptopkg "github.com/certctl-io/certctl/internal/crypto"
 	"github.com/certctl-io/certctl/internal/repository"
 )
 
@@ -22,46 +23,66 @@ import (
 // (oidc_pre_login_sessions.absolute_expires_at default of
 // NOW() + INTERVAL '10 minutes') AND re-checked at the service
 // layer at consume time.
+//
+// Audit 2026-05-10 HIGH-5 closure — state, nonce, and pkce_verifier
+// are encrypted at rest using v3 AES-256-GCM (per-row salt + nonce)
+// via internal/crypto.EncryptIfKeySet. The encryption key reuses
+// CERTCTL_CONFIG_ENCRYPTION_KEY. The legacy plaintext columns are
+// kept nullable for backward compat with in-flight handshakes during
+// rolling deploys; the new write path NEVER populates them.
 // =============================================================================
 
 // PreLoginRepository is the postgres implementation of
 // repository.PreLoginRepository.
 type PreLoginRepository struct {
 	db            *sql.DB
+	encryptionKey string
 }
 
 // NewPreLoginRepository constructs a PreLoginRepository.
-func NewPreLoginRepository(db *sql.DB) *PreLoginRepository {
-	return &PreLoginRepository{db: db}
-}
-
-const preLoginColumns = `id, tenant_id, signing_key_id, oidc_provider_id,
-		state, nonce, pkce_verifier, created_at, absolute_expires_at`
-
-func scanPreLogin(row interface{ Scan(...interface{}) error }) (*repository.PreLoginSession, error) {
-	var p repository.PreLoginSession
-	if err := row.Scan(
-		&p.ID, &p.TenantID, &p.SigningKeyID, &p.OIDCProviderID,
-		&p.State, &p.Nonce, &p.PKCEVerifier, &p.CreatedAt, &p.AbsoluteExpiresAt,
-	); err != nil {
-		return nil, err
-	}
-	return &p, nil
+//
+// Audit 2026-05-10 HIGH-5: encryptionKey is the same
+// CERTCTL_CONFIG_ENCRYPTION_KEY value already used for OIDC client
+// secrets and SessionSigningKey material. An empty key is rejected at
+// startup by config validation; if the repo is constructed with an
+// empty key here it will fail-closed at write time (see Create), so
+// pre-login rows can never be silently persisted plaintext.
+func NewPreLoginRepository(db *sql.DB, encryptionKey string) *PreLoginRepository {
+	return &PreLoginRepository{db: db, encryptionKey: encryptionKey}
 }
 
 // Create persists a pre-login row. Caller MUST have already generated
 // the random id (`pl-<base64url>`), state, nonce, and PKCE verifier.
 // CreatedAt + AbsoluteExpiresAt default to NOW() / NOW()+10min when
 // zero (the schema's DEFAULT clauses handle this).
+//
+// Audit 2026-05-10 HIGH-5: state / nonce / pkce_verifier are encrypted
+// before INSERT via crypto.EncryptIfKeySet. The plaintext columns are
+// left NULL — they remain on the schema only for in-flight backward
+// compat with pre-deploy code paths that still write them, and will
+// be dropped in a follow-up migration after the rolling deploy.
 func (r *PreLoginRepository) Create(ctx context.Context, p *repository.PreLoginSession) error {
+	stateEnc, _, serr := cryptopkg.EncryptIfKeySet([]byte(p.State), r.encryptionKey)
+	if serr != nil {
+		return fmt.Errorf("oidc_pre_login encrypt state: %w", serr)
+	}
+	nonceEnc, _, nerr := cryptopkg.EncryptIfKeySet([]byte(p.Nonce), r.encryptionKey)
+	if nerr != nil {
+		return fmt.Errorf("oidc_pre_login encrypt nonce: %w", nerr)
+	}
+	verifierEnc, _, verr := cryptopkg.EncryptIfKeySet([]byte(p.PKCEVerifier), r.encryptionKey)
+	if verr != nil {
+		return fmt.Errorf("oidc_pre_login encrypt pkce_verifier: %w", verr)
+	}
+
 	if p.CreatedAt.IsZero() && p.AbsoluteExpiresAt.IsZero() {
 		_, err := r.db.ExecContext(ctx, `
 			INSERT INTO oidc_pre_login_sessions (
 				id, tenant_id, signing_key_id, oidc_provider_id,
-				state, nonce, pkce_verifier
+				state_enc, nonce_enc, pkce_verifier_enc
 			) VALUES ($1,$2,$3,$4,$5,$6,$7)`,
 			p.ID, p.TenantID, p.SigningKeyID, p.OIDCProviderID,
-			p.State, p.Nonce, p.PKCEVerifier)
+			stateEnc, nonceEnc, verifierEnc)
 		if err != nil {
 			return fmt.Errorf("oidc_pre_login create: %w", err)
 		}
@@ -77,10 +98,10 @@ func (r *PreLoginRepository) Create(ctx context.Context, p *repository.PreLoginS
 	_, err := r.db.ExecContext(ctx, `
 		INSERT INTO oidc_pre_login_sessions (
 			id, tenant_id, signing_key_id, oidc_provider_id,
-			state, nonce, pkce_verifier, created_at, absolute_expires_at
+			state_enc, nonce_enc, pkce_verifier_enc, created_at, absolute_expires_at
 		) VALUES ($1,$2,$3,$4,$5,$6,$7,$8,$9)`,
 		p.ID, p.TenantID, p.SigningKeyID, p.OIDCProviderID,
-		p.State, p.Nonce, p.PKCEVerifier, p.CreatedAt, p.AbsoluteExpiresAt)
+		stateEnc, nonceEnc, verifierEnc, p.CreatedAt, p.AbsoluteExpiresAt)
 	if err != nil {
 		return fmt.Errorf("oidc_pre_login create: %w", err)
 	}
@@ -98,22 +119,77 @@ func (r *PreLoginRepository) Create(ctx context.Context, p *repository.PreLoginS
 // against concurrent callers — the second caller racing with a
 // successful first caller gets ErrPreLoginNotFound, never a duplicate
 // session-mint.
+//
+// Audit 2026-05-10 HIGH-5: prefer the encrypted columns
+// (state_enc / nonce_enc / pkce_verifier_enc); fall back to the
+// legacy plaintext columns ONLY when the encrypted columns are NULL
+// (in-flight rows from pre-deploy code paths during a rolling
+// deploy). After 000042 drops the plaintext columns, the fallback is
+// dead code.
 func (r *PreLoginRepository) LookupAndConsume(ctx context.Context, id string) (*repository.PreLoginSession, error) {
 	row := r.db.QueryRowContext(ctx, `
 		DELETE FROM oidc_pre_login_sessions WHERE id = $1
-		RETURNING `+preLoginColumns,
+		RETURNING id, tenant_id, signing_key_id, oidc_provider_id,
+		          state, nonce, pkce_verifier,
+		          state_enc, nonce_enc, pkce_verifier_enc,
+		          created_at, absolute_expires_at`,
 		id)
-	p, err := scanPreLogin(row)
-	if err != nil {
+
+	var p repository.PreLoginSession
+	var statePlain, noncePlain, verifierPlain sql.NullString
+	var stateEnc, nonceEnc, verifierEnc []byte
+	if err := row.Scan(
+		&p.ID, &p.TenantID, &p.SigningKeyID, &p.OIDCProviderID,
+		&statePlain, &noncePlain, &verifierPlain,
+		&stateEnc, &nonceEnc, &verifierEnc,
+		&p.CreatedAt, &p.AbsoluteExpiresAt,
+	); err != nil {
 		if errors.Is(err, sql.ErrNoRows) {
 			return nil, repository.ErrPreLoginNotFound
 		}
 		return nil, fmt.Errorf("oidc_pre_login lookup_and_consume: %w", err)
 	}
+
+	// Prefer encrypted columns; fall back to legacy plaintext only
+	// when encrypted is NULL (rolling-deploy compat).
+	if state, err := r.materialize(stateEnc, statePlain); err != nil {
+		return nil, fmt.Errorf("oidc_pre_login decrypt state: %w", err)
+	} else {
+		p.State = state
+	}
+	if nonce, err := r.materialize(nonceEnc, noncePlain); err != nil {
+		return nil, fmt.Errorf("oidc_pre_login decrypt nonce: %w", err)
+	} else {
+		p.Nonce = nonce
+	}
+	if verifier, err := r.materialize(verifierEnc, verifierPlain); err != nil {
+		return nil, fmt.Errorf("oidc_pre_login decrypt pkce_verifier: %w", err)
+	} else {
+		p.PKCEVerifier = verifier
+	}
+
 	if time.Now().UTC().After(p.AbsoluteExpiresAt) {
 		return nil, repository.ErrPreLoginExpired
 	}
-	return p, nil
+	return &p, nil
+}
+
+// materialize returns the decrypted value when the encrypted blob is
+// present; otherwise falls back to the legacy plaintext column for
+// rolling-deploy compat. Returns an error when both are absent —
+// inconsistent row state that should never persist beyond a deploy.
+func (r *PreLoginRepository) materialize(enc []byte, plain sql.NullString) (string, error) {
+	if len(enc) > 0 {
+		decrypted, err := cryptopkg.DecryptIfKeySet(enc, r.encryptionKey)
+		if err != nil {
+			return "", err
+		}
+		return string(decrypted), nil
+	}
+	if plain.Valid {
+		return plain.String, nil
+	}
+	return "", errors.New("row missing both encrypted and plaintext value")
 }
 
 // GarbageCollectExpired deletes rows whose absolute_expires_at is in

internal/repository/postgres/oidc_prelogin_encryption_test.go

@@ -0,0 +1,206 @@
+package postgres_test
+
+import (
+	"bytes"
+	"context"
+	"testing"
+
+	cryptopkg "github.com/certctl-io/certctl/internal/crypto"
+	"github.com/certctl-io/certctl/internal/repository"
+	"github.com/certctl-io/certctl/internal/repository/postgres"
+)
+
+// Audit 2026-05-10 HIGH-5 closure — pin the at-rest invariant for
+// the OIDC pre-login table. Pre-fix, state / nonce / pkce_verifier
+// rode plaintext columns; an operator restoring an unredacted backup
+// to a debug environment leaked every in-flight handshake. Post-fix,
+// the new write path encrypts via crypto.EncryptIfKeySet (v3 magic
+// 0x03 || salt(16) || nonce(12) || ciphertext+tag). The legacy
+// plaintext columns remain on the schema (nullable) for in-flight
+// rolling-deploy compat; the new write path NEVER populates them.
+//
+// Mirror of the Phase 13 oidc_providers encryption-invariant pattern.
+// Lives in the postgres_test package so it runs against the real
+// migrated schema via testcontainers; protected by testing.Short().
+
+const (
+	preLoginEncTestPassphrase = "high-5-prelogin-test-encryption-key-DO-NOT-USE-IN-PROD"
+)
+
+// TestPreLoginRepository_EncryptionInvariant_HIGH5 pins three legs:
+//
+//	(a) the {state,nonce,pkce_verifier}_enc columns contain v3
+//	    AES-GCM blobs (NOT the plaintext) immediately after Create;
+//	(b) the legacy plaintext columns are NULL after the new write
+//	    path runs (defense against a regressing patch that re-adds
+//	    plaintext writes);
+//	(c) LookupAndConsume round-trips the original plaintext via the
+//	    encrypted columns, returning state / nonce / pkce_verifier
+//	    byte-for-byte equal to the values written.
+func TestPreLoginRepository_EncryptionInvariant_HIGH5(t *testing.T) {
+	if testing.Short() {
+		t.Skip("HIGH-5 encryption invariant: integration test in short mode")
+	}
+	db := getTestDB(t).freshSchema(t)
+	ctx := context.Background()
+
+	// Seed a session_signing_keys row + an oidc_providers row so the
+	// pre-login row's FK constraints are satisfied. The signing-key
+	// material can be any non-empty byte slice (the pre-login repo
+	// doesn't decrypt it).
+	if _, err := db.ExecContext(ctx, `
+		INSERT INTO session_signing_keys (id, tenant_id, key_material_encrypted)
+		VALUES ('sk-high5', 't-default', $1)`,
+		[]byte{0x03, 0x00, 0x01, 0x02}); err != nil {
+		t.Fatalf("seed session_signing_keys: %v", err)
+	}
+	provRepo := postgres.NewOIDCProviderRepository(db)
+	if err := provRepo.Create(ctx, newValidProvider("high5")); err != nil {
+		t.Fatalf("seed oidc_provider: %v", err)
+	}
+
+	repo := postgres.NewPreLoginRepository(db, preLoginEncTestPassphrase)
+
+	statePlain := "very-secret-oidc-state-do-not-leak"
+	noncePlain := "very-secret-oidc-nonce-do-not-leak"
+	verifierPlain := "very-secret-pkce-verifier-bytes-do-not-leak"
+
+	row := &repository.PreLoginSession{
+		ID:             "pl-high5-1",
+		TenantID:       "t-default",
+		SigningKeyID:   "sk-high5",
+		OIDCProviderID: "op-high5",
+		State:          statePlain,
+		Nonce:          noncePlain,
+		PKCEVerifier:   verifierPlain,
+	}
+	if err := repo.Create(ctx, row); err != nil {
+		t.Fatalf("Create: %v", err)
+	}
+
+	// ── Invariant (a): encrypted columns contain v3 blobs, NOT plaintext. ──
+	var stateEnc, nonceEnc, verifierEnc []byte
+	if err := db.QueryRowContext(ctx, `
+		SELECT state_enc, nonce_enc, pkce_verifier_enc
+		FROM oidc_pre_login_sessions WHERE id = $1`, row.ID).
+		Scan(&stateEnc, &nonceEnc, &verifierEnc); err != nil {
+		t.Fatalf("SELECT raw enc columns: %v", err)
+	}
+	for label, blob := range map[string][]byte{
+		"state":         stateEnc,
+		"nonce":         nonceEnc,
+		"pkce_verifier": verifierEnc,
+	} {
+		if len(blob) == 0 {
+			t.Errorf("INVARIANT (a) VIOLATED: %s_enc is empty post-Create", label)
+			continue
+		}
+		// v3 magic + salt(16) + nonce(12) + at least 16 bytes for the AEAD tag.
+		if len(blob) < 1+16+12+16 {
+			t.Errorf("INVARIANT (a) VIOLATED: %s_enc blob too short (%d bytes)", label, len(blob))
+		}
+		if blob[0] != 0x03 {
+			t.Errorf("INVARIANT (a) VIOLATED: %s_enc magic = 0x%02x; want 0x03 (v3)", label, blob[0])
+		}
+	}
+	if bytes.Contains(stateEnc, []byte(statePlain)) {
+		t.Errorf("INVARIANT (a) VIOLATED: state_enc contains plaintext substring %q", statePlain)
+	}
+	if bytes.Contains(nonceEnc, []byte(noncePlain)) {
+		t.Errorf("INVARIANT (a) VIOLATED: nonce_enc contains plaintext substring %q", noncePlain)
+	}
+	if bytes.Contains(verifierEnc, []byte(verifierPlain)) {
+		t.Errorf("INVARIANT (a) VIOLATED: pkce_verifier_enc contains plaintext substring %q", verifierPlain)
+	}
+
+	// ── Invariant (b): legacy plaintext columns are NULL post-Create. ──
+	var statePlainCol, noncePlainCol, verifierPlainCol *string
+	if err := db.QueryRowContext(ctx, `
+		SELECT state, nonce, pkce_verifier
+		FROM oidc_pre_login_sessions WHERE id = $1`, row.ID).
+		Scan(&statePlainCol, &noncePlainCol, &verifierPlainCol); err != nil {
+		t.Fatalf("SELECT plaintext columns: %v", err)
+	}
+	if statePlainCol != nil {
+		t.Errorf("INVARIANT (b) VIOLATED: legacy state column = %q; want NULL", *statePlainCol)
+	}
+	if noncePlainCol != nil {
+		t.Errorf("INVARIANT (b) VIOLATED: legacy nonce column = %q; want NULL", *noncePlainCol)
+	}
+	if verifierPlainCol != nil {
+		t.Errorf("INVARIANT (b) VIOLATED: legacy pkce_verifier column = %q; want NULL", *verifierPlainCol)
+	}
+
+	// ── Invariant (c): LookupAndConsume round-trips the plaintext. ──
+	got, err := repo.LookupAndConsume(ctx, row.ID)
+	if err != nil {
+		t.Fatalf("LookupAndConsume: %v", err)
+	}
+	if got.State != statePlain {
+		t.Errorf("INVARIANT (c) VIOLATED: round-trip state = %q; want %q", got.State, statePlain)
+	}
+	if got.Nonce != noncePlain {
+		t.Errorf("INVARIANT (c) VIOLATED: round-trip nonce = %q; want %q", got.Nonce, noncePlain)
+	}
+	if got.PKCEVerifier != verifierPlain {
+		t.Errorf("INVARIANT (c) VIOLATED: round-trip pkce_verifier = %q; want %q", got.PKCEVerifier, verifierPlain)
+	}
+
+	// Sanity: a wrong passphrase MUST fail the AEAD check.
+	if _, err := cryptopkg.DecryptIfKeySet(stateEnc, preLoginEncTestPassphrase+"-wrong"); err == nil {
+		t.Error("AEAD broken: DecryptIfKeySet succeeded with wrong passphrase")
+	}
+}
+
+// TestPreLoginRepository_EncryptionInvariant_LegacyPlaintextStillReadable
+// pins the rolling-deploy fallback. Pre-deploy code paths that already
+// wrote a row using the legacy schema (plaintext columns populated,
+// _enc columns NULL) must continue to consume cleanly. After 000042
+// drops the plaintext columns, this test should be deleted along with
+// the materialize() fallback in the repo.
+func TestPreLoginRepository_EncryptionInvariant_LegacyPlaintextStillReadable(t *testing.T) {
+	if testing.Short() {
+		t.Skip("HIGH-5 legacy fallback: integration test in short mode")
+	}
+	db := getTestDB(t).freshSchema(t)
+	ctx := context.Background()
+
+	if _, err := db.ExecContext(ctx, `
+		INSERT INTO session_signing_keys (id, tenant_id, key_material_encrypted)
+		VALUES ('sk-legacy', 't-default', $1)`,
+		[]byte{0x03, 0x00, 0x01, 0x02}); err != nil {
+		t.Fatalf("seed session_signing_keys: %v", err)
+	}
+	provRepo := postgres.NewOIDCProviderRepository(db)
+	if err := provRepo.Create(ctx, newValidProvider("legacy")); err != nil {
+		t.Fatalf("seed oidc_provider: %v", err)
+	}
+
+	// Simulate a legacy-write row (plaintext populated, _enc NULL) by
+	// inserting directly via SQL — this is the byte shape the pre-fix
+	// code path produced.
+	if _, err := db.ExecContext(ctx, `
+		INSERT INTO oidc_pre_login_sessions (
+			id, tenant_id, signing_key_id, oidc_provider_id,
+			state, nonce, pkce_verifier
+		) VALUES ($1, $2, $3, $4, $5, $6, $7)`,
+		"pl-legacy-1", "t-default", "sk-legacy", "op-legacy",
+		"legacy-state", "legacy-nonce", "legacy-verifier"); err != nil {
+		t.Fatalf("legacy direct INSERT: %v", err)
+	}
+
+	repo := postgres.NewPreLoginRepository(db, preLoginEncTestPassphrase)
+	got, err := repo.LookupAndConsume(ctx, "pl-legacy-1")
+	if err != nil {
+		t.Fatalf("LookupAndConsume legacy row: %v", err)
+	}
+	if got.State != "legacy-state" {
+		t.Errorf("legacy round-trip state = %q; want legacy-state", got.State)
+	}
+	if got.Nonce != "legacy-nonce" {
+		t.Errorf("legacy round-trip nonce = %q; want legacy-nonce", got.Nonce)
+	}
+	if got.PKCEVerifier != "legacy-verifier" {
+		t.Errorf("legacy round-trip pkce_verifier = %q; want legacy-verifier", got.PKCEVerifier)
+	}
+}

migrations/000041_prelogin_encrypted.down.sql

@@ -0,0 +1,21 @@
+-- =============================================================================
+-- Rollback for 000041_prelogin_encrypted.up.sql.
+--
+-- Drops the {state,nonce,pkce_verifier}_enc columns and re-adds the NOT NULL
+-- constraint on the plaintext columns. Safe because no in-flight rows persist
+-- past the 10-minute TTL — the GC sweep removes legacy rows quickly.
+-- =============================================================================
+
+ALTER TABLE oidc_pre_login_sessions
+    DROP COLUMN IF EXISTS state_enc,
+    DROP COLUMN IF EXISTS nonce_enc,
+    DROP COLUMN IF EXISTS pkce_verifier_enc;
+
+-- Re-applying NOT NULL would fail if there are any rows missing the plaintext;
+-- truncate the table to remove any stragglers (only handshake-state, safe).
+TRUNCATE TABLE oidc_pre_login_sessions;
+
+ALTER TABLE oidc_pre_login_sessions
+    ALTER COLUMN state          SET NOT NULL,
+    ALTER COLUMN nonce          SET NOT NULL,
+    ALTER COLUMN pkce_verifier  SET NOT NULL;

migrations/000041_prelogin_encrypted.up.sql

@@ -0,0 +1,38 @@
+-- =============================================================================
+-- 2026-05-10 Audit / HIGH-5 closure
+-- =============================================================================
+--
+-- Pre-login rows in oidc_pre_login_sessions used to persist OIDC state, nonce,
+-- and the PKCE verifier as plaintext columns. An operator restoring a backup
+-- to a debug environment without redacting handshake-table data leaked every
+-- in-flight verifier; combined with a separately-leaked authorization code
+-- (e.g. logged at a misconfigured TLS terminator), the attacker could exchange
+-- code + verifier directly. RFC 7636 §7 requires verifier confidentiality.
+--
+-- This migration adds {state,nonce,pkce_verifier}_enc BYTEA columns alongside
+-- the existing plaintext columns. The new repository write path emits only the
+-- encrypted columns (via internal/crypto.EncryptIfKeySet, v3 blob format —
+-- magic(0x03) || salt(16) || nonce(12) || ciphertext+tag, AES-256-GCM with
+-- per-row salt + nonce). The existing plaintext columns are made nullable so
+-- the new write path doesn't have to populate them; in-flight handshakes from
+-- pre-deploy code paths still consume the legacy plaintext columns until the
+-- 10-minute absolute TTL expires every legacy row.
+--
+-- A follow-up migration (queued for v2.1.1) drops the plaintext columns once
+-- the rolling deploy completes. We do NOT bundle the DROP into 000041 because
+-- in-flight handshakes during deploy would break.
+--
+-- The encryption key reuses CERTCTL_CONFIG_ENCRYPTION_KEY — the same passphrase
+-- already protecting OIDC client secrets, session signing keys, and other
+-- secret-bearing rows. No new env var.
+-- =============================================================================
+
+ALTER TABLE oidc_pre_login_sessions
+    ADD COLUMN IF NOT EXISTS state_enc          BYTEA,
+    ADD COLUMN IF NOT EXISTS nonce_enc          BYTEA,
+    ADD COLUMN IF NOT EXISTS pkce_verifier_enc  BYTEA;
+
+ALTER TABLE oidc_pre_login_sessions
+    ALTER COLUMN state          DROP NOT NULL,
+    ALTER COLUMN nonce          DROP NOT NULL,
+    ALTER COLUMN pkce_verifier  DROP NOT NULL;