feat: instance administration, bootstrap admin, and managed-tier OAuth gate

Self-hosted instances are now email/password only — OAuth providers
(GitHub/Google/Discord/Microsoft) activate solely when PRIMORA_MANAGED=true,
reserved for the future hosted tier.

Sign-up lifecycle: the first public sign-up becomes the instance admin; after
bootstrap, sign-up closes by default. A better-auth databaseHook gates only
/sign-up/email, so admin-created users and OAuth flows bypass it. The login
page reads GET /instance/public to hide the sign-up tab, show the bootstrap
notice, and render only the providers the instance offers.

Instance settings live in core.settings (migration 00010) and resolve
in-app > env > built-in default, cached 15s. Platform admins (better-auth
user.role) manage sign-up, mail transport, and rate limits via
GET/PUT/DELETE /instance/settings or the new Settings → Instance tab. Secret
values are AES-256-GCM encrypted at rest with PRIMORA_ENCRYPTION_KEY, never
returned by the API, and decrypted by the auth service at send time.

Auth service reads the same settings table for the sign-up gate and mail
config, so in-app changes take effect without a restart.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/db/migrations/00010_settings.sql

@@ -0,0 +1,14 @@
+-- +goose Up
+-- Instance-level settings. In-app values override env vars; secrets are
+-- AES-256-GCM ciphertext (base64) produced by the backend's Encryptor and
+-- readable by the auth service, which shares PRIMORA_ENCRYPTION_KEY.
+CREATE TABLE core.settings (
+  key TEXT PRIMARY KEY,
+  value JSONB NOT NULL,
+  secret BOOLEAN NOT NULL DEFAULT FALSE,
+  updated_by TEXT,
+  updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- +goose Down
+DROP TABLE IF EXISTS core.settings;

apps/backend/db/queries/settings.sql

@@ -0,0 +1,18 @@
+-- name: GetSetting :one
+SELECT key, value, secret, updated_at FROM core.settings WHERE key = $1;
+
+-- name: ListSettings :many
+SELECT key, value, secret, updated_at FROM core.settings ORDER BY key;
+
+-- name: UpsertSetting :one
+INSERT INTO core.settings (key, value, secret, updated_by)
+VALUES ($1, $2::jsonb, $3, $4)
+ON CONFLICT (key) DO UPDATE
+SET value = EXCLUDED.value,
+    secret = EXCLUDED.secret,
+    updated_by = EXCLUDED.updated_by,
+    updated_at = NOW()
+RETURNING *;
+
+-- name: DeleteSetting :exec
+DELETE FROM core.settings WHERE key = $1;

apps/backend/internal/app/app.go

@@ -92,6 +92,7 @@ func Bootstrap(ctx context.Context) (*App, error) {
 		return nil, fmt.Errorf("encryption key: %w", err)
 	}
 	platform := services.NewPlatformService(repo, store, services.NewMailer(cfg), os.Getenv("VITE_APP_URL"), dbxClient, encryptor, logger)
+	settings := services.NewSettingsService(repo, encryptor)
 
 	if cfg.Env == "production" {
 		gin.SetMode(gin.ReleaseMode)
@@ -126,10 +127,12 @@ func Bootstrap(ctx context.Context) (*App, error) {
 			APIKeyPerMinute: cfg.APIKeyRateLimitPerMin,
 			UserPerMinute:   cfg.UserRateLimitPerMin,
 		},
+		RateLimitResolver: settings.RateLimitPerMinute,
 	}.ResolveActor())
 
 	handler := &handlers.HTTPHandler{
 		Platform: platform,
+		Settings: settings,
 		Validate: validator.New(),
 		Metrics:  metrics,
 		Readiness: func(c *gin.Context) map[string]any {

apps/backend/internal/database/db/models.go

@@ -336,6 +336,14 @@ type CoreScheduledJobRun struct {
 	FinishedAt  pgtype.Timestamptz `json:"finished_at"`
 }
 
+type CoreSetting struct {
+	Key       string             `json:"key"`
+	Value     []byte             `json:"value"`
+	Secret    bool               `json:"secret"`
+	UpdatedBy *string            `json:"updated_by"`
+	UpdatedAt pgtype.Timestamptz `json:"updated_at"`
+}
+
 type CoreUser struct {
 	ID            uuid.UUID          `json:"id"`
 	AuthSubject   string             `json:"auth_subject"`

apps/backend/internal/database/db/querier.go

@@ -46,6 +46,7 @@ type Querier interface {
 	DeletePendingInvitationByIDForOrganization(ctx context.Context, arg DeletePendingInvitationByIDForOrganizationParams) (CoreProjectInvitation, error)
 	DeleteProjectByID(ctx context.Context, id uuid.UUID) (CoreProject, error)
 	DeleteScheduledJob(ctx context.Context, arg DeleteScheduledJobParams) (uuid.UUID, error)
+	DeleteSetting(ctx context.Context, key string) error
 	DeleteWebhook(ctx context.Context, arg DeleteWebhookParams) (CoreWebhook, error)
 	EventTotals(ctx context.Context, arg EventTotalsParams) (EventTotalsRow, error)
 	EventTypeSeries(ctx context.Context, arg EventTypeSeriesParams) ([]EventTypeSeriesRow, error)
@@ -68,6 +69,7 @@ type Querier interface {
 	GetProjectMembership(ctx context.Context, arg GetProjectMembershipParams) (GetProjectMembershipRow, error)
 	GetProjectOverview(ctx context.Context, id uuid.UUID) (GetProjectOverviewRow, error)
 	GetScheduledJobByID(ctx context.Context, id uuid.UUID) (CoreScheduledJob, error)
+	GetSetting(ctx context.Context, key string) (GetSettingRow, error)
 	GetUserByAuthSubject(ctx context.Context, authSubject string) (CoreUser, error)
 	GetUserByID(ctx context.Context, id uuid.UUID) (CoreUser, error)
 	GetWebhookByID(ctx context.Context, id uuid.UUID) (CoreWebhook, error)
@@ -97,6 +99,7 @@ type Querier interface {
 	ListProjectsForOrganization(ctx context.Context, arg ListProjectsForOrganizationParams) ([]ListProjectsForOrganizationRow, error)
 	ListScheduledJobRuns(ctx context.Context, arg ListScheduledJobRunsParams) ([]CoreScheduledJobRun, error)
 	ListScheduledJobs(ctx context.Context, projectID uuid.UUID) ([]CoreScheduledJob, error)
+	ListSettings(ctx context.Context) ([]ListSettingsRow, error)
 	ListWebhookDeliveries(ctx context.Context, arg ListWebhookDeliveriesParams) ([]CoreWebhookDelivery, error)
 	ListWebhooks(ctx context.Context, projectID uuid.UUID) ([]CoreWebhook, error)
 	ListWebhooksForEvent(ctx context.Context, arg ListWebhooksForEventParams) ([]CoreWebhook, error)
@@ -132,6 +135,7 @@ type Querier interface {
 	UpdateScheduledJob(ctx context.Context, arg UpdateScheduledJobParams) (CoreScheduledJob, error)
 	UpdateWebhook(ctx context.Context, arg UpdateWebhookParams) (CoreWebhook, error)
 	UpsertComponent(ctx context.Context, arg UpsertComponentParams) (CoreComponent, error)
+	UpsertSetting(ctx context.Context, arg UpsertSettingParams) (CoreSetting, error)
 	UpsertUser(ctx context.Context, arg UpsertUserParams) (CoreUser, error)
 }
 

apps/backend/internal/database/db/settings.sql.go

@@ -0,0 +1,116 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.29.0
+// source: settings.sql
+
+package db
+
+import (
+	"context"
+
+	"github.com/jackc/pgx/v5/pgtype"
+)
+
+const deleteSetting = `-- name: DeleteSetting :exec
+DELETE FROM core.settings WHERE key = $1
+`
+
+func (q *Queries) DeleteSetting(ctx context.Context, key string) error {
+	_, err := q.db.Exec(ctx, deleteSetting, key)
+	return err
+}
+
+const getSetting = `-- name: GetSetting :one
+SELECT key, value, secret, updated_at FROM core.settings WHERE key = $1
+`
+
+type GetSettingRow struct {
+	Key       string             `json:"key"`
+	Value     []byte             `json:"value"`
+	Secret    bool               `json:"secret"`
+	UpdatedAt pgtype.Timestamptz `json:"updated_at"`
+}
+
+func (q *Queries) GetSetting(ctx context.Context, key string) (GetSettingRow, error) {
+	row := q.db.QueryRow(ctx, getSetting, key)
+	var i GetSettingRow
+	err := row.Scan(
+		&i.Key,
+		&i.Value,
+		&i.Secret,
+		&i.UpdatedAt,
+	)
+	return i, err
+}
+
+const listSettings = `-- name: ListSettings :many
+SELECT key, value, secret, updated_at FROM core.settings ORDER BY key
+`
+
+type ListSettingsRow struct {
+	Key       string             `json:"key"`
+	Value     []byte             `json:"value"`
+	Secret    bool               `json:"secret"`
+	UpdatedAt pgtype.Timestamptz `json:"updated_at"`
+}
+
+func (q *Queries) ListSettings(ctx context.Context) ([]ListSettingsRow, error) {
+	rows, err := q.db.Query(ctx, listSettings)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []ListSettingsRow
+	for rows.Next() {
+		var i ListSettingsRow
+		if err := rows.Scan(
+			&i.Key,
+			&i.Value,
+			&i.Secret,
+			&i.UpdatedAt,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const upsertSetting = `-- name: UpsertSetting :one
+INSERT INTO core.settings (key, value, secret, updated_by)
+VALUES ($1, $2::jsonb, $3, $4)
+ON CONFLICT (key) DO UPDATE
+SET value = EXCLUDED.value,
+    secret = EXCLUDED.secret,
+    updated_by = EXCLUDED.updated_by,
+    updated_at = NOW()
+RETURNING key, value, secret, updated_by, updated_at
+`
+
+type UpsertSettingParams struct {
+	Key       string  `json:"key"`
+	Column2   []byte  `json:"column_2"`
+	Secret    bool    `json:"secret"`
+	UpdatedBy *string `json:"updated_by"`
+}
+
+func (q *Queries) UpsertSetting(ctx context.Context, arg UpsertSettingParams) (CoreSetting, error) {
+	row := q.db.QueryRow(ctx, upsertSetting,
+		arg.Key,
+		arg.Column2,
+		arg.Secret,
+		arg.UpdatedBy,
+	)
+	var i CoreSetting
+	err := row.Scan(
+		&i.Key,
+		&i.Value,
+		&i.Secret,
+		&i.UpdatedBy,
+		&i.UpdatedAt,
+	)
+	return i, err
+}

apps/backend/internal/handlers/http.go

@@ -20,6 +20,7 @@ import (
 
 type HTTPHandler struct {
 	Platform  *services.PlatformService
+	Settings  *services.SettingsService
 	Validate  *validator.Validate
 	Metrics   *observability.Metrics
 	Readiness func(*gin.Context) map[string]any
@@ -33,6 +34,10 @@ func (h *HTTPHandler) Register(router *gin.Engine) {
 
 	api := router.Group("/api/v1")
 	api.GET("/me", h.me)
+	api.GET("/instance/public", h.instancePublic)
+	api.GET("/instance/settings", h.listInstanceSettings)
+	api.PUT("/instance/settings/:key", h.updateInstanceSetting)
+	api.DELETE("/instance/settings/:key", h.deleteInstanceSetting)
 	api.POST("/bootstrap", h.bootstrap)
 	api.GET("/organizations", h.organizations)
 	api.POST("/organizations", h.createOrganization)

apps/backend/internal/handlers/instance.go

@@ -0,0 +1,132 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+	"os"
+
+	"github.com/gin-gonic/gin"
+
+	"github.com/tdvorak/primora/apps/backend/internal/middleware"
+	apperrors "github.com/tdvorak/primora/apps/backend/internal/response"
+	"github.com/tdvorak/primora/apps/backend/internal/services"
+)
+
+// instancePublic serves unauthenticated bootstrap state to the login page.
+// It intentionally exposes only what the sign-in UI needs.
+func (h *HTTPHandler) instancePublic(c *gin.Context) {
+	users, err := h.Settings.AuthUserCount(c.Request.Context())
+	if err != nil {
+		apperrors.Abort(c, http.StatusInternalServerError, "settings_unavailable", err.Error())
+		return
+	}
+	signupEnabled := false
+	if users > 0 {
+		signupEnabled, err = h.Settings.GetBool(c.Request.Context(), "auth.signup_enabled")
+		if err != nil {
+			apperrors.Abort(c, http.StatusInternalServerError, "settings_unavailable", err.Error())
+			return
+		}
+	}
+	c.JSON(http.StatusOK, gin.H{
+		"signup_enabled":     signupEnabled,
+		"bootstrap_required": users == 0,
+		"social_providers":   managedSocialProviders(),
+	})
+}
+
+// managedSocialProviders mirrors the auth service's managed gate: OAuth only
+// exists when PRIMORA_MANAGED=true and the provider's client id is set.
+func managedSocialProviders() []string {
+	if os.Getenv("PRIMORA_MANAGED") != "true" {
+		return []string{}
+	}
+	providers := []string{}
+	for _, p := range []struct{ name, envKey string }{
+		{"github", "GITHUB_CLIENT_ID"},
+		{"google", "GOOGLE_CLIENT_ID"},
+		{"discord", "DISCORD_CLIENT_ID"},
+		{"microsoft", "MICROSOFT_CLIENT_ID"},
+	} {
+		if os.Getenv(p.envKey) != "" {
+			providers = append(providers, p.name)
+		}
+	}
+	return providers
+}
+
+// requireInstanceAdmin gates handlers on the platform admin role (better-auth
+// `user.role`), which is distinct from org/project roles.
+func (h *HTTPHandler) requireInstanceAdmin(c *gin.Context) bool {
+	actor, ok := middleware.RequireActor(c)
+	if !ok {
+		return false
+	}
+	if !actor.IsUser() || !h.Settings.IsAdmin(c.Request.Context(), actor.AuthSubject) {
+		apperrors.Abort(c, http.StatusForbidden, "admin_required", "instance admin role required")
+		return false
+	}
+	return true
+}
+
+func (h *HTTPHandler) listInstanceSettings(c *gin.Context) {
+	if !h.requireInstanceAdmin(c) {
+		return
+	}
+	settings, err := h.Settings.ListResolved(c.Request.Context())
+	if err != nil {
+		apperrors.Abort(c, http.StatusInternalServerError, "settings_unavailable", err.Error())
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"settings": settings})
+}
+
+func (h *HTTPHandler) updateInstanceSetting(c *gin.Context) {
+	if !h.requireInstanceAdmin(c) {
+		return
+	}
+	key := c.Param("key")
+	if _, ok := services.SettingSpecs[key]; !ok {
+		apperrors.Abort(c, http.StatusNotFound, "unknown_setting", "unknown setting key")
+		return
+	}
+	var body struct {
+		Value json.RawMessage `json:"value" binding:"required"`
+	}
+	if err := c.ShouldBindJSON(&body); err != nil || len(body.Value) == 0 {
+		apperrors.Abort(c, http.StatusBadRequest, "invalid_body", "expected {\"value\": ...}")
+		return
+	}
+	actor, _ := middleware.ActorFromContext(c)
+	if err := h.Settings.Store(c.Request.Context(), key, body.Value, actor.Email); err != nil {
+		apperrors.Abort(c, http.StatusBadRequest, "invalid_value", err.Error())
+		return
+	}
+	value, source, err := h.Settings.Resolve(c.Request.Context(), key)
+	if err != nil {
+		apperrors.Abort(c, http.StatusInternalServerError, "settings_unavailable", err.Error())
+		return
+	}
+	spec := services.SettingSpecs[key]
+	resp := gin.H{"key": key, "type": spec.Type, "secret": spec.Secret, "is_set": true, "source": source}
+	if !spec.Secret {
+		resp["value"] = value
+	}
+	c.JSON(http.StatusOK, resp)
+}
+
+func (h *HTTPHandler) deleteInstanceSetting(c *gin.Context) {
+	if !h.requireInstanceAdmin(c) {
+		return
+	}
+	key := c.Param("key")
+	if _, ok := services.SettingSpecs[key]; !ok {
+		apperrors.Abort(c, http.StatusNotFound, "unknown_setting", "unknown setting key")
+		return
+	}
+	if err := h.Settings.Delete(c.Request.Context(), key); err != nil {
+		apperrors.Abort(c, http.StatusInternalServerError, "settings_unavailable", err.Error())
+		return
+	}
+	c.Status(http.StatusNoContent)
+}

apps/backend/internal/middleware/context.go

@@ -37,6 +37,9 @@ type AuthMiddleware struct {
 	Redis      *redis.Client
 	Verifier   *auth.Verifier
 	RateLimits RateLimitConfig
+	// RateLimitResolver overrides RateLimits with live instance settings when
+	// set — it resolves "user" and "api_key" limits per request (cached).
+	RateLimitResolver func(ctx context.Context, scope string) int
 }
 
 type RateLimitConfig struct {
@@ -44,6 +47,16 @@ type RateLimitConfig struct {
 	UserPerMinute   int
 }
 
+func (m AuthMiddleware) rateLimit(ctx context.Context, scope string, fallback int) int {
+	if m.RateLimitResolver == nil {
+		return fallback
+	}
+	if v := m.RateLimitResolver(ctx, scope); v >= 0 {
+		return v
+	}
+	return fallback
+}
+
 func RequestID() gin.HandlerFunc {
 	return func(c *gin.Context) {
 		requestID := c.Request.Header.Get("X-Request-ID")
@@ -105,7 +118,7 @@ func (m AuthMiddleware) ResolveActor() gin.HandlerFunc {
 				if actor.UserID != nil {
 					userIdentity = actor.UserID.String()
 				}
-				if !m.enforceRateLimit(c, "user", userIdentity, m.RateLimits.UserPerMinute, "User rate limit exceeded") {
+				if !m.enforceRateLimit(c, "user", userIdentity, m.rateLimit(c.Request.Context(), "user", m.RateLimits.UserPerMinute), "User rate limit exceeded") {
 					return
 				}
 				c.Set(actorKey, actor)
@@ -123,7 +136,7 @@ func (m AuthMiddleware) ResolveActor() gin.HandlerFunc {
 				apperrors.Abort(c, http.StatusUnauthorized, "invalid_api_key", err.Error())
 				return
 			}
-			if !m.enforceRateLimit(c, "apikey", actor.APIKeyPrefix, m.RateLimits.APIKeyPerMinute, "API key rate limit exceeded") {
+			if !m.enforceRateLimit(c, "apikey", actor.APIKeyPrefix, m.rateLimit(c.Request.Context(), "api_key", m.RateLimits.APIKeyPerMinute), "API key rate limit exceeded") {
 				return
 			}
 			if need := requiredAPIKeyScope(c.Request.Method, c.Request.URL.Path); !actor.HasScope(need) {

apps/backend/internal/repositories/core_repository.go

@@ -56,3 +56,35 @@ func (r *CoreRepository) GetAPIKeyByPrefix(ctx context.Context, prefix string) (
 func (r *CoreRepository) TouchAPIKey(ctx context.Context, id uuid.UUID) error {
 	return r.queries.TouchAPIKey(ctx, id)
 }
+
+// Auth-user lookups hit the better-auth tables in the public schema. They are
+// raw queries on purpose: sqlc only knows the core schema, and a view would
+// break when the backend migrates before the auth service has created its
+// tables.
+func (r *CoreRepository) GetAuthUserRole(ctx context.Context, authSubject string) (string, error) {
+	var role string
+	err := r.pool.QueryRow(ctx, `select coalesce(role, 'user') from public."user" where id = $1`, authSubject).Scan(&role)
+	return role, err
+}
+
+func (r *CoreRepository) CountAuthUsers(ctx context.Context) (int64, error) {
+	var n int64
+	err := r.pool.QueryRow(ctx, `select count(*) from public."user"`).Scan(&n)
+	return n, err
+}
+
+func (r *CoreRepository) GetSetting(ctx context.Context, key string) (db.GetSettingRow, error) {
+	return r.queries.GetSetting(ctx, key)
+}
+
+func (r *CoreRepository) ListSettings(ctx context.Context) ([]db.ListSettingsRow, error) {
+	return r.queries.ListSettings(ctx)
+}
+
+func (r *CoreRepository) UpsertSetting(ctx context.Context, params db.UpsertSettingParams) (db.CoreSetting, error) {
+	return r.queries.UpsertSetting(ctx, params)
+}
+
+func (r *CoreRepository) DeleteSetting(ctx context.Context, key string) error {
+	return r.queries.DeleteSetting(ctx, key)
+}

apps/backend/internal/services/settings.go

@@ -0,0 +1,345 @@
+package services
+
+import (
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"sort"
+	"strconv"
+	"sync"
+	"time"
+
+	"github.com/jackc/pgx/v5"
+
+	db "github.com/tdvorak/primora/apps/backend/internal/database/db"
+	"github.com/tdvorak/primora/apps/backend/internal/repositories"
+	"github.com/tdvorak/primora/apps/backend/internal/secrets"
+)
+
+// SettingSpec describes a settable instance key: value type, the env var used
+// as fallback when no DB row exists, and a built-in default.
+type SettingSpec struct {
+	Key     string
+	Type    string // "bool" | "int" | "string"
+	Secret  bool
+	EnvKey  string
+	Default string
+}
+
+// SettingSpecs is the registry of keys manageable in-app. Env vars stay as
+// defaults — an app value wins when present.
+var SettingSpecs = map[string]SettingSpec{
+	"auth.signup_enabled":         {Key: "auth.signup_enabled", Type: "bool", EnvKey: "SIGNUP_ENABLED", Default: "false"},
+	"mail.from":                   {Key: "mail.from", Type: "string", EnvKey: "MAIL_FROM", Default: "Primora <[email protected]>"},
+	"mail.resend_api_key":         {Key: "mail.resend_api_key", Type: "string", Secret: true, EnvKey: "RESEND_API_KEY"},
+	"mail.smtp_host":              {Key: "mail.smtp_host", Type: "string", EnvKey: "SMTP_HOST"},
+	"mail.smtp_port":              {Key: "mail.smtp_port", Type: "int", EnvKey: "SMTP_PORT", Default: "1025"},
+	"mail.smtp_user":              {Key: "mail.smtp_user", Type: "string", EnvKey: "SMTP_USER"},
+	"mail.smtp_password":          {Key: "mail.smtp_password", Type: "string", Secret: true, EnvKey: "SMTP_PASSWORD"},
+	"mail.smtp_secure":            {Key: "mail.smtp_secure", Type: "bool", EnvKey: "SMTP_SECURE", Default: "false"},
+	"ratelimit.user_per_minute":   {Key: "ratelimit.user_per_minute", Type: "int", EnvKey: "USER_RATE_LIMIT_PER_MINUTE", Default: "240"},
+	"ratelimit.api_key_per_minute": {Key: "ratelimit.api_key_per_minute", Type: "int", EnvKey: "API_KEY_RATE_LIMIT_PER_MINUTE", Default: "600"},
+}
+
+const settingsCacheTTL = 15 * time.Second
+
+// resolvedSetting holds the stored string form: plaintext for normal keys,
+// base64 ciphertext for secrets — Resolve() decrypts on read.
+type resolvedSetting struct {
+	value  string
+	secret bool
+}
+
+// SettingsService resolves instance settings: DB row > env var > default.
+// Values cache briefly so per-request consumers (rate limits) stay cheap.
+type SettingsService struct {
+	repo      *repositories.CoreRepository
+	encryptor *secrets.Encryptor
+
+	mu      sync.Mutex
+	cache   map[string]resolvedSetting
+	cacheAt time.Time
+}
+
+func NewSettingsService(repo *repositories.CoreRepository, encryptor *secrets.Encryptor) *SettingsService {
+	return &SettingsService{repo: repo, encryptor: encryptor}
+}
+
+// Resolve returns the effective string value plus its source
+// ("app" | "env" | "default"). Secret DB values are decrypted.
+func (s *SettingsService) Resolve(ctx context.Context, key string) (value, source string, err error) {
+	spec, ok := SettingSpecs[key]
+	if !ok {
+		return "", "", fmt.Errorf("unknown setting: %s", key)
+	}
+	row, err := s.stored(ctx, key)
+	if err != nil {
+		return "", "", err
+	}
+	if row != nil {
+		raw := row.value
+		if row.secret {
+			raw, err = s.decrypt(raw)
+			if err != nil {
+				return "", "", fmt.Errorf("decrypt %s: %w", key, err)
+			}
+		}
+		return raw, "app", nil
+	}
+	if env := os.Getenv(spec.EnvKey); env != "" {
+		return env, "env", nil
+	}
+	return spec.Default, "default", nil
+}
+
+func (s *SettingsService) GetBool(ctx context.Context, key string) (bool, error) {
+	raw, _, err := s.Resolve(ctx, key)
+	if err != nil {
+		return false, err
+	}
+	v, err := strconv.ParseBool(raw)
+	if err != nil {
+		return false, fmt.Errorf("setting %s is not a bool: %q", key, raw)
+	}
+	return v, nil
+}
+
+func (s *SettingsService) GetInt(ctx context.Context, key string) (int, error) {
+	raw, _, err := s.Resolve(ctx, key)
+	if err != nil {
+		return 0, err
+	}
+	v, err := strconv.Atoi(raw)
+	if err != nil {
+		return 0, fmt.Errorf("setting %s is not an int: %q", key, raw)
+	}
+	return v, nil
+}
+
+// RateLimitPerMinute is the hot-path helper for the auth middleware.
+func (s *SettingsService) RateLimitPerMinute(ctx context.Context, scope string) int {
+	key := "ratelimit.user_per_minute"
+	if scope == "api_key" {
+		key = "ratelimit.api_key_per_minute"
+	}
+	v, err := s.GetInt(ctx, key)
+	if err != nil {
+		spec := SettingSpecs[key]
+		fallback, _ := strconv.Atoi(spec.Default)
+		return fallback
+	}
+	return v
+}
+
+// ValidateAndStore type-checks the raw JSON value against the registry and
+// persists it. Secret values are encrypted before they touch the DB.
+func (s *SettingsService) Store(ctx context.Context, key string, raw json.RawMessage, updatedBy string) error {
+	spec, ok := SettingSpecs[key]
+	if !ok {
+		return fmt.Errorf("unknown setting: %s", key)
+	}
+	plain, err := normalizeSetting(spec, raw)
+	if err != nil {
+		return err
+	}
+	value := []byte(strconv.Quote(plain))
+	if spec.Secret {
+		ciphertext, err := s.encryptor.Encrypt([]byte(plain))
+		if err != nil {
+			return fmt.Errorf("encrypt %s: %w", key, err)
+		}
+		value = []byte(strconv.Quote(base64.StdEncoding.EncodeToString(ciphertext)))
+	}
+	_, err = s.repo.UpsertSetting(ctx, db.UpsertSettingParams{
+		Key:       key,
+		Column2:   value,
+		Secret:    spec.Secret,
+		UpdatedBy: &updatedBy,
+	})
+	if err != nil {
+		return err
+	}
+	s.invalidate()
+	return nil
+}
+
+func (s *SettingsService) Delete(ctx context.Context, key string) error {
+	if _, ok := SettingSpecs[key]; !ok {
+		return fmt.Errorf("unknown setting: %s", key)
+	}
+	if err := s.repo.DeleteSetting(ctx, key); err != nil {
+		return err
+	}
+	s.invalidate()
+	return nil
+}
+
+// IsAdmin reports whether the actor holds the platform admin role
+// (better-auth `user.role`), not an org/project role.
+func (s *SettingsService) IsAdmin(ctx context.Context, authSubject string) bool {
+	role, err := s.repo.GetAuthUserRole(ctx, authSubject)
+	return err == nil && role == "admin"
+}
+
+func (s *SettingsService) AuthUserCount(ctx context.Context) (int64, error) {
+	return s.repo.CountAuthUsers(ctx)
+}
+
+// ListResolved returns every registered key with its effective state.
+// Secret values are masked — never returned.
+func (s *SettingsService) ListResolved(ctx context.Context) ([]ResolvedSetting, error) {
+	stored, err := s.loadStored(ctx)
+	if err != nil {
+		return nil, err
+	}
+	out := make([]ResolvedSetting, 0, len(SettingSpecs))
+	for _, key := range sortedSettingKeys() {
+		spec := SettingSpecs[key]
+		entry := ResolvedSetting{Key: key, Secret: spec.Secret, Type: spec.Type}
+		if row, ok := stored[key]; ok {
+			entry.IsSet = true
+			entry.Source = "app"
+			if !spec.Secret {
+				entry.Value = json.RawMessage(strconv.Quote(row.value))
+			}
+		} else if env := os.Getenv(spec.EnvKey); env != "" {
+			entry.Source = "env"
+			if !spec.Secret {
+				entry.Value = json.RawMessage(strconv.Quote(env))
+			}
+		} else {
+			entry.Source = "default"
+			if !spec.Secret {
+				entry.Value = json.RawMessage(strconv.Quote(spec.Default))
+			}
+		}
+		out = append(out, entry)
+	}
+	return out, nil
+}
+
+type ResolvedSetting struct {
+	Key    string          `json:"key"`
+	Type   string          `json:"type"`
+	Secret bool            `json:"secret"`
+	IsSet  bool            `json:"is_set"`
+	Source string          `json:"source"`
+	Value  json.RawMessage `json:"value,omitempty"`
+}
+
+func sortedSettingKeys() []string {
+	keys := make([]string, 0, len(SettingSpecs))
+	for k := range SettingSpecs {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys
+}
+
+func (s *SettingsService) loadStored(ctx context.Context) (map[string]resolvedSetting, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.cache != nil && time.Since(s.cacheAt) < settingsCacheTTL {
+		return s.cache, nil
+	}
+	rows, err := s.repo.ListSettings(ctx)
+	if err != nil {
+		return nil, err
+	}
+	fresh := make(map[string]resolvedSetting, len(rows))
+	for _, r := range rows {
+		encoded, err := unwrapSettingValue(r.Value)
+		if err != nil {
+			continue // unreadable row — treat as unset rather than break consumers
+		}
+		fresh[r.Key] = resolvedSetting{value: encoded, secret: r.Secret}
+	}
+	s.cache = fresh
+	s.cacheAt = time.Now()
+	return fresh, nil
+}
+
+func (s *SettingsService) stored(ctx context.Context, key string) (*resolvedSetting, error) {
+	all, err := s.loadStored(ctx)
+	if err != nil {
+		// cold-cache fallback: direct lookup
+		row, err := s.repo.GetSetting(ctx, key)
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, nil
+		}
+		if err != nil {
+			return nil, err
+		}
+		encoded, err := unwrapSettingValue(row.Value)
+		if err != nil {
+			return nil, err
+		}
+		return &resolvedSetting{value: encoded, secret: row.Secret}, nil
+	}
+	if row, ok := all[key]; ok {
+		return &row, nil
+	}
+	return nil, nil
+}
+
+func (s *SettingsService) decrypt(ciphertextB64 string) (string, error) {
+	raw, err := base64.StdEncoding.DecodeString(ciphertextB64)
+	if err != nil {
+		return "", err
+	}
+	plain, err := s.encryptor.Decrypt(raw)
+	if err != nil {
+		return "", err
+	}
+	return string(plain), nil
+}
+
+func (s *SettingsService) invalidate() {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.cache = nil
+}
+
+// unwrapSettingValue decodes the JSONB column: every stored value is a JSON
+// string — the plaintext for normal keys, base64 ciphertext for secrets.
+func unwrapSettingValue(raw []byte) (string, error) {
+	var encoded string
+	if err := json.Unmarshal(raw, &encoded); err != nil {
+		return "", err
+	}
+	return encoded, nil
+}
+
+// normalizeSetting validates raw JSON against the spec type and returns the
+// canonical string form stored/compared internally.
+func normalizeSetting(spec SettingSpec, raw json.RawMessage) (string, error) {
+	switch spec.Type {
+	case "bool":
+		var v bool
+		if err := json.Unmarshal(raw, &v); err != nil {
+			return "", fmt.Errorf("%s expects a boolean", spec.Key)
+		}
+		return strconv.FormatBool(v), nil
+	case "int":
+		var v int
+		if err := json.Unmarshal(raw, &v); err != nil {
+			return "", fmt.Errorf("%s expects an integer", spec.Key)
+		}
+		if v < 0 {
+			return "", fmt.Errorf("%s must be >= 0", spec.Key)
+		}
+		return strconv.Itoa(v), nil
+	default:
+		var v string
+		if err := json.Unmarshal(raw, &v); err != nil {
+			return "", fmt.Errorf("%s expects a string", spec.Key)
+		}
+		if len(v) > 512 {
+			return "", fmt.Errorf("%s exceeds 512 chars", spec.Key)
+		}
+		return v, nil
+	}
+}

apps/backend/internal/services/settings_test.go

@@ -0,0 +1,68 @@
+package services
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestNormalizeSetting(t *testing.T) {
+	t.Parallel()
+
+	boolSpec := SettingSpecs["auth.signup_enabled"]
+	intSpec := SettingSpecs["ratelimit.user_per_minute"]
+	strSpec := SettingSpecs["mail.smtp_host"]
+
+	cases := []struct {
+		name    string
+		spec    SettingSpec
+		raw     string
+		want    string
+		wantErr bool
+	}{
+		{name: "bool true", spec: boolSpec, raw: `true`, want: "true"},
+		{name: "bool false", spec: boolSpec, raw: `false`, want: "false"},
+		{name: "bool rejects string", spec: boolSpec, raw: `"true"`, wantErr: true},
+		{name: "bool rejects int", spec: boolSpec, raw: `1`, wantErr: true},
+		{name: "int accepts", spec: intSpec, raw: `120`, want: "120"},
+		{name: "int zero allowed", spec: intSpec, raw: `0`, want: "0"},
+		{name: "int rejects negative", spec: intSpec, raw: `-5`, wantErr: true},
+		{name: "int rejects float", spec: intSpec, raw: `1.5`, wantErr: true},
+		{name: "int rejects string", spec: intSpec, raw: `"120"`, wantErr: true},
+		{name: "string accepts", spec: strSpec, raw: `"smtp.example.com"`, want: "smtp.example.com"},
+		{name: "string rejects number", spec: strSpec, raw: `42`, wantErr: true},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got, err := normalizeSetting(tc.spec, json.RawMessage(tc.raw))
+			if tc.wantErr {
+				if err == nil {
+					t.Fatalf("expected error, got %q", got)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if got != tc.want {
+				t.Fatalf("got %q, want %q", got, tc.want)
+			}
+		})
+	}
+}
+
+func TestSortedSettingKeysDeterministic(t *testing.T) {
+	t.Parallel()
+
+	first := sortedSettingKeys()
+	second := sortedSettingKeys()
+	if len(first) != len(SettingSpecs) {
+		t.Fatalf("expected %d keys, got %d", len(SettingSpecs), len(first))
+	}
+	for i := range first {
+		if first[i] != second[i] {
+			t.Fatalf("key order not deterministic at %d: %q vs %q", i, first[i], second[i])
+		}
+	}
+}

apps/backend/openapi/openapi.yaml

@@ -17,6 +17,7 @@ tags:
   - name: Integrations
   - name: Webhooks
   - name: Automation
+  - name: Instance
 paths:
   /health/liveness:
     get:
@@ -67,6 +68,87 @@ paths:
                 $ref: "#/components/schemas/MeResponse"
         "401":
           $ref: "#/components/responses/ErrorResponse"
+  /instance/public:
+    get:
+      tags: [Instance]
+      operationId: getInstancePublic
+      summary: Public instance state for the login page — no auth required
+      responses:
+        "200":
+          description: Public instance configuration
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/InstancePublicConfig"
+  /instance/settings:
+    get:
+      tags: [Instance]
+      operationId: listInstanceSettings
+      summary: List instance settings (platform admin only)
+      security:
+        - bearerAuth: []
+      responses:
+        "200":
+          description: Resolved instance settings
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/InstanceSettingsResponse"
+        "401":
+          $ref: "#/components/responses/ErrorResponse"
+        "403":
+          $ref: "#/components/responses/ErrorResponse"
+  /instance/settings/{key}:
+    put:
+      tags: [Instance]
+      operationId: updateInstanceSetting
+      summary: Set an instance setting override (platform admin only)
+      security:
+        - bearerAuth: []
+      parameters:
+        - name: key
+          in: path
+          required: true
+          schema:
+            type: string
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/UpdateInstanceSettingRequest"
+      responses:
+        "200":
+          description: Setting stored
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/InstanceSetting"
+        "400":
+          $ref: "#/components/responses/ErrorResponse"
+        "403":
+          $ref: "#/components/responses/ErrorResponse"
+        "404":
+          $ref: "#/components/responses/ErrorResponse"
+    delete:
+      tags: [Instance]
+      operationId: deleteInstanceSetting
+      summary: Revert a setting to its env/default value (platform admin only)
+      security:
+        - bearerAuth: []
+      parameters:
+        - name: key
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        "204":
+          description: Setting reverted
+        "403":
+          $ref: "#/components/responses/ErrorResponse"
+        "404":
+          $ref: "#/components/responses/ErrorResponse"
   /bootstrap:
     post:
       tags: [Platform]
@@ -1952,6 +2034,54 @@ components:
               type: string
           required: [code, message]
       required: [status, error]
+    InstancePublicConfig:
+      type: object
+      properties:
+        signup_enabled:
+          type: boolean
+          description: Whether public sign-up is open (bootstrap always allowed)
+        bootstrap_required:
+          type: boolean
+          description: True when no user exists yet — first sign-up becomes instance admin
+        social_providers:
+          type: array
+          items:
+            type: string
+          description: Enabled OAuth providers — empty on self-hosted
+      required: [signup_enabled, bootstrap_required, social_providers]
+    InstanceSetting:
+      type: object
+      properties:
+        key:
+          type: string
+        type:
+          type: string
+          enum: [bool, int, string]
+        secret:
+          type: boolean
+        is_set:
+          type: boolean
+          description: True when an in-app override exists
+        source:
+          type: string
+          enum: [app, env, default]
+        value:
+          description: Effective value — never returned for secret keys
+      required: [key, type, secret, is_set, source]
+    InstanceSettingsResponse:
+      type: object
+      properties:
+        settings:
+          type: array
+          items:
+            $ref: "#/components/schemas/InstanceSetting"
+      required: [settings]
+    UpdateInstanceSettingRequest:
+      type: object
+      properties:
+        value:
+          description: JSON value matching the key's declared type
+      required: [value]
     BootstrapRequest:
       type: object
       properties: