Effect Integration

Better Auth uses Web Standard Request and Response objects. Effect 4 can mount auth.handler with HttpEffect.fromWebHandler.

Before you begin, configure a Better Auth instance.

Install Effect

npm install effect

If you're starting a new Effect project, follow the Effect installation guide.

Mount the auth handler

The example below runs on Node.js. See the Effect Platform guide to use another runtime.

npm install @effect/platform-node

src/index.ts

import { createServer } from "node:http";
import { NodeHttpServer, NodeRuntime } from "@effect/platform-node";
import { Layer } from "effect";
import { HttpEffect, HttpRouter, HttpServerResponse } from "effect/http";
import { auth } from "./auth.ts";

const homeRoute = HttpRouter.add(
  "GET",
  "/",
  HttpServerResponse.text("Hello Better Auth"),
);

const authRoutes = HttpRouter.add( 
  "*", 
  "/api/auth/*", // Match your Better Auth basePath.
  HttpEffect.fromWebHandler(auth.handler), 
); 

const routes = Layer.mergeAll(homeRoute, authRoutes);

const server = HttpRouter.serve(routes).pipe(
  Layer.provide(NodeHttpServer.layer(createServer, { port: 3000 })),
);

Layer.launch(server).pipe(NodeRuntime.runMain);

If your frontend runs on a different origin, allow it in both the Effect server's CORS middleware and Better Auth's trustedOrigins. The middleware applies to every route, so list only the origins that need cookie access.

src/auth.ts

import { betterAuth } from "better-auth";

export const auth = betterAuth({
  trustedOrigins: ["http://localhost:5173"], 
});

src/index.ts

import { HttpMiddleware } from "effect/http";

const server = HttpRouter.serve(routes, {
  middleware: HttpMiddleware.cors({
    allowedOrigins: ["http://localhost:5173"], 
    credentials: true,
  }),
}).pipe(
  Layer.provide(NodeHttpServer.layer(createServer, { port: 3000 })),
);

For cross-site cookies, see Cookies.

Protect application routes

You can protect application resources by checking the session with Better Auth:

src/index.ts

import { Effect } from "effect";
import { HttpServerRequest, HttpServerResponse } from "effect/http";

const profileRoute = HttpRouter.add(
  "GET",
  "/profile",
  Effect.gen(function* () {
    const request = yield* HttpServerRequest.HttpServerRequest;
    const session = yield* Effect.tryPromise(() =>
      auth.api.getSession({ headers: request.headers }),
    );

    if (!session) {
      return HttpServerResponse.empty({ status: 401 });
    }

    return yield* HttpServerResponse.json(session.user);
  }),
);

const routes = Layer.mergeAll(homeRoute, authRoutes, profileRoute);

Install Effect

Mount the auth handler

Cross-origin requests

Protect application routes

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