Mapping Existing Columns

Instead of altering your existing database column names, you can map them to match Better Auth’s expected structure. This allows you to retain your current database schema.

User Schema

Map the following fields in the user schema:

• (next-auth v4) emailVerified: datetime → boolean

Session Schema

Map the following fields in the session schema:

• expires → expiresAt
• sessionToken → token
• (next-auth v4) add createdAt with datetime type
• (next-auth v4) add updatedAt with datetime type

Make sure to have createdAt and updatedAt fields on your session schema.

Account Schema

Map these fields in the account schema:

• (next-auth v4) provider → providerId
• providerAccountId → accountId
• refresh_token → refreshToken
• access_token → accessToken
• (next-auth v3) access_token_expires → accessTokenExpiresAt and int → datetime
• (next-auth v4) expires_at → accessTokenExpiresAt and int → datetime
• id_token → idToken
• (next-auth v4) add createdAt with datetime type
• (next-auth v4) add updatedAt with datetime type

Remove the session_state, type, and token_type fields, as they are not required by Better Auth.

export const auth = betterAuth({
  // Other configs
  account: {
    fields: {
      accountId: "providerAccountId",
      refreshToken: "refresh_token",
      accessToken: "access_token",
      accessTokenExpiresAt: "access_token_expires",
      idToken: "id_token",
    },
  },
})

Note: If you use ORM adapters, you can map these fields in your schema file.

Example with Prisma:

model Session {
    id          String   @id @default(cuid())
    expiresAt   DateTime @map("expires") // Map your existing `expires` field to Better Auth's `expiresAt`
    token       String   @map("sessionToken") // Map your existing `sessionToken` field to Better Auth's `token`
    userId      String
    user        User     @relation(fields: [userId], references: [id])
}

Make sure to have createdAt and updatedAt fields on your account schema.

Update the Route Handler

In the app/api/auth folder, rename the [...nextauth] file to [...all] to avoid confusion. Then, update the route.ts file as follows:

import { toNextJsHandler } from "better-auth/next-js"
import { auth } from "~/server/auth"
 
export const { POST, GET } = toNextJsHandler(auth)

Update the Client

Create a file named auth-client.ts in the lib folder. Add the following code:

import { createAuthClient } from "better-auth/react"
 
export const authClient = createAuthClient({
  baseURL: process.env.BASE_URL!, // Optional if the API base URL matches the frontend
})
 
export const { signIn, signOut, useSession } = authClient

Social Login

Update your social login actions to use Better Auth. For example, for Discord:

import { signIn } from "~/lib/auth-client"
 
export const signInDiscord = async () => {
  const data = await signIn.social({
    provider: "discord",
  })
  return data
}

Update useSession Calls

Replace useSession calls with Better Auth’s version. Example:

import { useSession } from "~/lib/auth-client";
 
export const Profile = () => {
    const { data } = useSession();
    return (
        <div>
            <pre>
                {JSON.stringify(data, null, 2)}
            </pre>
        </div>
    );
};

Server-Side Session Handling

Use the auth instance to get session data on the server:

"use server"
 
import { auth } from "~/server/auth"
import { headers } from "next/headers"
 
export const protectedAction = async () => {
  const session = await auth.api.getSession({
    headers: await headers(),
  })
}

Middleware

To protect routes with middleware, refer to the Next.js middleware guide.