gerbeur/api/middleware/auth.ts

import {
  type Next,
  type RouteParams,
  type RouterContext,
  type State,
} from "@oak/oak";
import { authenticate } from "../lib/auth.ts";
import { APIErrorCode } from "../../shared/api.ts";
import { APIException } from "../lib/api-exception.ts";
import type { AuthPayload } from "../model/auth.ts";
import { can } from "../lib/permissions.ts";
import type { Permission } from "../../shared/permissions.ts";

export interface AuthState extends State {
  user: AuthPayload;
}

// A router context whose state is guaranteed to carry the authenticated user
// (populated by authMiddleware). Generic over the route path so `ctx.params`
// stays typed per-route — e.g. `AuthContext<"/:userId/role">`.
export type AuthContext<
  R extends string = string,
  P extends RouteParams<R> = RouteParams<R>,
> = RouterContext<R, P, AuthState>;

export async function authMiddleware<R extends string>(
  ctx: AuthContext<R>,
  next: Next,
): Promise<void> {
  const authHeader = ctx.request.headers.get("Authorization");

  if (!authHeader || !authHeader.startsWith("Bearer ")) {
    throw new APIException(
      APIErrorCode.UNAUTHORIZED,
      401,
      "Missing or invalid token",
    );
  }

  const token = authHeader.substring(7);
  // Also checks the user still exists and hasn't changed their password since
  // the token was issued, and takes the live role from the DB.
  const payload = await authenticate(token);

  if (!payload) {
    throw new APIException(APIErrorCode.UNAUTHORIZED, 401, "Invalid token");
  }

  ctx.state.user = payload;

  await next();
}

export async function adminOnlyMiddleware<R extends string>(
  ctx: AuthContext<R>,
  next: Next,
): Promise<void> {
  if (ctx.state.user.role !== "admin") {
    throw new APIException(
      APIErrorCode.UNAUTHORIZED,
      403,
      "Admin access required",
    );
  }

  await next();
}

// Gates a route on a named permission. Must run after authMiddleware. Generic
// over the route path so it composes with path-typed route handlers.
export function requirePermission(permission: Permission) {
  return async <R extends string>(
    ctx: AuthContext<R>,
    next: Next,
  ): Promise<void> => {
    if (!ctx.state.user || !can(ctx.state.user, permission)) {
      throw new APIException(
        APIErrorCode.UNAUTHORIZED,
        403,
        "Insufficient permissions",
      );
    }
    await next();
  };
}