TanStack Start Integration

This integration guide is assuming you are using TanStack Start.

Before you start, make sure you have a Better Auth instance configured. If you haven't done that yet, check out the installation.

Mount the handler

We need to mount the handler to a TanStack API endpoint/Server Route. Create a new file: /src/routes/api/auth/$.ts

src/routes/api/auth/$.ts
import { auth } from '@/lib/auth' // import your auth instance
import { createServerFileRoute } from '@tanstack/react-start/server'
 
export const ServerRoute = createServerFileRoute('/api/auth/$').methods({
  GET: ({ request }) => {
    return auth.handler(request)
  },
  POST: ({ request }) => {
    return auth.handler(request)
  },
})

If you haven't created your server route handler yet, you can do so by creating a file: /src/server.ts

src/server.ts
import {
  createStartHandler,
  defaultStreamHandler,
} from '@tanstack/react-start/server'
import { createRouter } from './router'
 
export default createStartHandler({
  createRouter,
})(defaultStreamHandler)

Usage tips

  • We recommend using the client SDK or authClient to handle authentication, rather than server actions with auth.api.
  • When you call functions that need to set cookies (like signInEmail or signUpEmail), you'll need to handle cookie setting for TanStack Start. Better Auth provides a reactStartCookies plugin to automatically handle this for you.
src/lib/auth.ts
import { betterAuth } from "better-auth";
import { reactStartCookies } from "better-auth/react-start";
 
export const auth = betterAuth({
    //...your config
    plugins: [reactStartCookies()] // make sure this is the last plugin in the array
})

Now, when you call functions that set cookies, they will be automatically set using TanStack Start's cookie handling system.

import { auth } from "@/lib/auth"
 
const signIn = async () => {
    await auth.api.signInEmail({
        body: {
            email: "user@email.com",
            password: "password",
        }
    })
}

SolidStart Integration

Integrate Better Auth with SolidStart.

Hono Integration

Integrate Better Auth with Hono.

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