Ekklesia/apps/api/src/app.ts

import {
  isAuthenticatedPrincipal,
  type ModuleRuntimeServices,
  type RegisteredModuleHttpRoute,
} from "@ekklesia/contracts";
import type {
  AuthorizationEvaluator,
  AuthorizationStore,
  PermissionRegistry,
} from "@ekklesia/core/authorization";
import { type EkklesiaIdentityRuntime, IdentityRuntimeError } from "@ekklesia/core/identity";
import { Hono } from "hono";
import type { Context, MiddlewareHandler } from "hono";
import { cors } from "hono/cors";
import { AUTH_REQUEST_MAX_BODY_BYTES, platformBodyLimit } from "./body-limits.js";
import { createGrantsRoutes } from "./grants-routes.js";
import { canonicalizeVaryHeader, mountModuleHttpRoutes } from "./module-http-routes.js";

export interface CreateApiAppAuthorizationOptions {
  readonly evaluator: AuthorizationEvaluator;
  /** The complete platform permission registry (Core's own declarations plus every installed
   * module's) — always the caller-composed registry `startApi` produces via
   * `prepareStartupModuleInventory`, never a Core-only fallback constructed here. */
  readonly registry: PermissionRegistry;
  readonly store: AuthorizationStore;
}

export interface CreateApiAppOptions {
  readonly authorization: CreateApiAppAuthorizationOptions;
  /** The started module runtime's published, immutable route snapshot — always the caller-started
   * runtime's exact `routes` (`startDiscoveredModuleRuntime`, `apps/api/src/server.ts`), mounted in
   * publication order under `/api/v1/modules/<module-id>`. Required rather than defaulted so a
   * caller not exercising modules must say so explicitly (an empty frozen array), never rely on an
   * implicit fallback. */
  readonly moduleRoutes: readonly RegisteredModuleHttpRoute[];
  /** The same frozen services object the caller's started module runtime already passed to every
   * module's `start`/`stop` hooks (`apps/api/src/server.ts`) — reference-identical, never a fresh
   * object built here, so a module's HTTP handlers and lifecycle hooks share exactly one
   * `ModuleDatabase` for the lifetime of this API runtime. */
  readonly moduleServices: ModuleRuntimeServices;
  readonly runtime: EkklesiaIdentityRuntime;
  /** Exact allowed browser origins. Never a wildcard; combined with `credentials: true`, only an
   * exact, reflected match is ever returned in `Access-Control-Allow-Origin`. Also the trusted set
   * `requireTrustedOrigin` checks for grant- and module-route-mutation routes — there is no second,
   * competing origin configuration. */
  readonly trustedOrigins: readonly string[];
}

function sanitizedErrorResponse(c: Context, error: unknown, status: 500 | 503) {
  const code = error instanceof IdentityRuntimeError ? error.code : "INTERNAL_ERROR";
  c.header("Cache-Control", "no-store");
  return c.json({ code }, status);
}

/**
 * Hono's own `cors()` unconditionally appends its own "Vary: Origin" after every response with a
 * dynamic-function `origin` — including one that already has its own `Vary` (module responses
 * force `Origin`/`Cookie`; `/api/v1/principal` sets `Origin, Cookie` directly; an `OPTIONS`
 * preflight sets its own) — so the header `cors()` itself leaves behind can still be an invalid
 * combined "*, Origin" or contain a case-different duplicate. This wraps `middleware` and
 * canonicalizes whatever `Vary` remains only *after* it has fully finished, using
 * `canonicalizeVaryHeader` — the same shared parsing/dedup primitive `mergedVaryHeader` (module
 * responses) builds on, so there is one implementation to keep in sync, not two that could diverge
 * — but never `mergedVaryHeader` itself: this boundary wraps *every* response, `OPTIONS` preflights
 * included, and must never inject `Origin`/`Cookie` onto a response that never had them, only
 * de-duplicate what is already there. Two return shapes have to be handled: a normal request lets
 * `middleware` call `next()` and mutate `c.res` in place, so the fix-up goes through `c.header()`
 * (reassigning `c.res` directly triggers Hono's own header-preserving merge and would silently
 * restore the uncanonicalized value); an `OPTIONS` preflight makes `cors()` return a new `Response`
 * directly without ever touching `c.res`, so the fix-up mutates that returned response's headers
 * instead. Neither path reads or clones the response body, so a streaming body is untouched either
 * way. Status, body, content type, ordinary headers, authorization, trusted-origin behavior, and
 * route ordering are all unaffected — only the final `Vary` value changes.
 */
function withCanonicalVary(middleware: MiddlewareHandler): MiddlewareHandler {
  return async (c, next) => {
    const result = await middleware(c, next);
    if (result instanceof Response) {
      const existingVary = result.headers.get("Vary");
      if (existingVary !== null) {
        result.headers.set("Vary", canonicalizeVaryHeader(existingVary));
      }
      return result;
    }
    const existingVary = c.res.headers.get("Vary");
    if (existingVary !== null) {
      c.header("Vary", canonicalizeVaryHeader(existingVary));
    }
    return result;
  };
}

/**
 * Pure Hono application factory: no I/O, no environment reads, no process side effects, and it
 * never invokes a module route handler while composing routes. Suitable for unit and integration
 * tests via `app.fetch` directly, with a fully injected identity runtime and authorization
 * evaluator/store standing in for real Better Auth/PostgreSQL where appropriate. Synchronously
 * throws `ModuleRouteConfigurationError` (`./module-http-routes.js`) if `moduleRoutes` and
 * `authorization.registry` are inconsistent — a route naming a permission the registry does not
 * register, which should never happen since both derive from the same discovered inventory, but is
 * checked explicitly rather than silently mounting an unenforceable route.
 */
export function createApiApp(options: CreateApiAppOptions): Hono {
  const { runtime } = options;
  const allowedOrigins = new Set(options.trustedOrigins);

  const app = new Hono();

  const corsMiddleware = withCanonicalVary(
    cors({
      allowHeaders: ["Content-Type"],
      allowMethods: ["GET", "POST", "PUT", "PATCH", "DELETE", "OPTIONS"],
      credentials: true,
      maxAge: 600,
      origin: (origin) => (origin && allowedOrigins.has(origin) ? origin : undefined),
    }),
  );
  app.use("/api/auth/*", corsMiddleware);
  app.use("/api/v1/*", corsMiddleware);

  const authBodyLimit = platformBodyLimit(AUTH_REQUEST_MAX_BODY_BYTES);
  app.on(["POST", "GET"], "/api/auth/*", authBodyLimit, async (c) => {
    try {
      const response = await runtime.handleAuthRequest(c.req.raw);
      // Every Better Auth response — including a session cookie — must never be cached by an
      // intermediary; constructing a fresh Response (rather than relying on `c.header()`, which
      // only affects `c.res`) guarantees this regardless of how the handler produced its result,
      // and never reads or buffers the body.
      const headers = new Headers(response.headers);
      headers.set("Cache-Control", "no-store");
      return new Response(response.body, {
        headers,
        status: response.status,
        statusText: response.statusText,
      });
    } catch (error) {
      return sanitizedErrorResponse(c, error, 500);
    }
  });

  app.get("/api/v1/principal", async (c) => {
    c.header("Cache-Control", "no-store");
    c.header("Vary", "Origin, Cookie");
    try {
      const principal = await runtime.resolvePrincipal(c.req.raw.headers);
      return c.json(
        isAuthenticatedPrincipal(principal)
          ? { kind: "authenticated" as const, userId: principal.userId }
          : { kind: "anonymous" as const },
        200,
      );
    } catch (error) {
      return sanitizedErrorResponse(c, error, 503);
    }
  });

  app.route(
    "/",
    createGrantsRoutes({
      evaluator: options.authorization.evaluator,
      registry: options.authorization.registry,
      runtime,
      store: options.authorization.store,
      trustedOrigins: allowedOrigins,
    }),
  );

  mountModuleHttpRoutes(app, options.moduleRoutes, {
    evaluator: options.authorization.evaluator,
    registry: options.authorization.registry,
    runtime,
    services: options.moduleServices,
    trustedOrigins: allowedOrigins,
  });

  app.notFound((c) => {
    c.header("Cache-Control", "no-store");
    return c.json({ code: "NOT_FOUND" }, 404);
  });
  app.onError((_error, c) => sanitizedErrorResponse(c, _error, 500));

  return app;
}